Optical film and image display device

ABSTRACT

An embodiment of the present invention provides an optical film ( 10 ) including a light-transmitting base material ( 11 ), a hard coat layer ( 12 ), and an inorganic layer ( 13 ) in this order, wherein the hard coat layer ( 12 ) is in contact with the inorganic layer ( 13 ), the hard coat layer ( 12 ) contains a binder resin ( 12 A) and inorganic particles ( 12 B), the hard coat layer ( 12 ) has a film thickness of 1 μm or more, and the hard coat layer ( 12 ) has an indentation hardness of 200 MPa or more.

CROSS-REFERENCE TO RELATED APPLICATION

The present application enjoys the benefit of priority to the priorJapanese Patent Application No. 2017-191319 (filed on Sep. 29, 2017),the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an optical film and image displaydevice.

BACKGROUND ART

Optical films are conventionally used for image display devices such assmartphones and tablet terminals. Examples of optical films to be usedinclude optical films having a light-transmitting base material, a hardcoat layer, and an inorganic layer in this order (see, for example,Patent Literature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Publication No.2016-128924

SUMMARY OF THE INVENTION

In some cases, however, such an optical film having an inorganic layerwill have the inorganic layer rubbed in a steel wool test in which thesurface of the inorganic layer is rubbed with steel wool with a grade of#0000 by reciprocating the steel wool with a load of 1 kg/cm² for 10times. In some other cases, the hard coat layer is chipped as well asthe inorganic layer is scratched.

The present invention is designed to solve the above problems. That is,an object of the present invention is to provide an optical film havingexcellent scratch resistance and an image display device including theoptical film.

The present invention includes the following inventions.

[1] An optical film including a hard coat layer and an inorganic layerin this order, wherein the hard coat layer is in contact with theinorganic layer, the hard coat layer contains a binder resin andinorganic particles, the hard coat layer has a film thickness of 1 μm ormore, and the hard coat layer has an indentation hardness of 200 MPa ormore.

[2] The optical film according to [1], wherein the inorganic particleshave an area ratio of 5% or more and 75% or less in the region up to adepth of 500 nm into the hard coat layer from the interface between thehard coat layer and the inorganic layer in the cross-section of the hardcoat layer in the film thickness direction.

[3] The optical film according to [1] or [2], wherein the inorganicparticles are silica particles.

[4] An optical film including a light-transmitting base material, a hardcoat layer, and an inorganic layer in this order, wherein the hard coatlayer is in contact with the inorganic layer, the hard coat layercontains at least one of a metallic element and a metalloid element, thehard coat layer has a film thickness of 1 μm or more, and the hard coatlayer has an indentation hardness of 200 MPa or more.

[5] The optical film according to any one of [1] to [4], wherein theinorganic layer is an inorganic oxide layer.

[6] The optical film according to any one of [1] to [4], wherein theinorganic layer contains silicon.

[7] The optical film according to any one of [1] to [6], wherein theinorganic layer has a thickness of 10 nm or more and 300 nm or less.

[8] The optical film according to any one of [4] to [7], wherein thehard coat layer contains a metalloid element, and the metalloid elementis silicon.

[9] The optical film according to any one of [4] to [8], wherein theatomic ratio of the total of the metallic element and the metalloidelement contained in the hard coat layer is 1.5% or more and 30% or lessas measured by X-ray photoelectron spectroscopy.

[10] The optical film according to any one of [1] to [9], wherein thehard coat layer contains a polymer of a polymerizable compoundcontaining a silsesquioxane having a polymerizable functional group.

[11] The optical film according to any one of [1] or [10], wherein nocrack or break is formed in the optical film after folding the opticalfilm at an angle of 180 degrees in a manner that leaves a gap of 6 mmbetween the opposite edges, unfolding the folded optical film, andrepeating the process one hundred thousand times.

[12] The optical film according to any one of [1] or [11], wherein nocrack or break is formed in the optical film after folding the opticalfilm with the inorganic layer facing inward at an angle of 180 degreesin a manner that leaves a gap of 2 mm between the opposite edges,unfolding the folded optical film, and repeating the process one hundredthousand times.

[13] The optical film according to any one of [1] to [12], wherein thelight-transmitting base material is composed of a polyimide resin, apolyamide resin, or a combination thereof.

[14] An image display device including a display panel and the opticalfilm according to any one of [1] to [13] placed on the observer's sideof the display panel, wherein the hard coat layer of the optical film isplaced on the observer's side of the light-transmitting base material.

[15] The image display device according to [14], wherein the displaypanel is an organic light emitting diode panel.

According to one aspect and another aspect of the present invention, anoptical film having excellent scratch resistance can be provided.According to still another aspect of the present invention, an imagedisplay device including such an optical film can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the schematic diagram of an optical film according to thefirst embodiment.

FIG. 2 depicts an enlarged view of a part of the optical film shown inFIG. 1.

FIGS. 3(A) to 3(C) schematically illustrate each step of the foldingtest.

FIG. 4 depicts the schematic diagram of an image display deviceaccording to the first embodiment.

FIG. 5 depicts the schematic diagram of an optical film according to thesecond embodiment.

FIG. 6 depicts the schematic diagram of an image display deviceaccording to the second embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

An optical film and an image display device according to the firstembodiment of the present invention are now described below withreference to the drawings. In this specification, the terms “film” and“sheet” are not distinguished from each other on the basis of thedifference of names alone. For example, the term “film” is thus used torefer inclusively to a member called “sheet.” FIG. 1 depicts a schematicdiagram of the optical film according to the present embodiment, FIG. 2depicts an enlarged view of a part of the optical film shown in FIG. 1,and FIGS. 3(A) to 3(C) schematically illustrate each step of the foldingtest.

The optical film 10 shown in FIG. 1 includes a light-transmitting basematerial 11, a hard coat layer 12, and an inorganic layer 13 in thisorder. The hard coat layer 12 is in contact with the inorganic layer 13.The optical film 10 further includes a functional layer 14 between thelight-transmitting base material 11 and the hard coat layer 12. Theoptical film 10 shown in FIG. 1 includes a functional layer 14, butanother optical film optionally includes no functional layer.

In FIG. 1, the surface 10A of the optical film 10 corresponds to thesurface 13A of the inorganic layer 13. In this specification, thesurface of the optical film is used to refer to one surface of theoptical film. Thus, the surface opposite to the surface of the opticalfilm will be referred to as the back surface, distinguished from thesurface of the optical film. The back surface 10B of the optical film 10corresponds to the opposite surface of the light-transmitting basematerial 11 from the hard coat layer 12 side.

The optical film 10 preferably has a haze value (total haze value) of2.5% or less. The optical film 10 having a haze value of 2.5% or lesscan obtain excellent transparency. A haze value of 1.5% or less or 1.0%or less is preferable increasingly in this order (the smaller the value,the more preferable).

The above-described haze value can be measured using a haze meter(product name “HM-150”; manufactured by Murakami Color ResearchLaboratory Co., Ltd.) in accordance with JIS K7136: 2000. Theabove-described haze value is defined as the arithmetic mean of threehaze values, wherein the three haze values are obtained by cutting apiece of 50 mm×100 mm from one optical film and placing the piece offilm without any curl or wrinkle and without any fingerprint or dirt,into the haze meter in such a manner that the inorganic layer side facesopposite to the light source to measure the haze value, and repeatingthe measurement three times. The phrase “measured three times” as usedherein should refer not to measuring at the same position three timesbut to measuring at three different positions. In the optical film 10,not only the surface 10A but also a laminated layer such as the hardcoat layer 12 is visually observed to be flat and also has a deviationin film thickness within ±10%. Accordingly, it is considered that anapproximate average haze value of the whole optical film can be obtainedby measuring the haze value at three different positions on the piececut out from the optical film. The deviation in haze value is within±10% even if a measurement object has a size as large as 1 m×3000 m orhas the same size as a 5-inch smartphone. If a piece having the samesize as described above cannot be cut out from the optical film, a piecehaving a sample size of 21 mm or more in diameter is required because,for example, the HM-150 haze meter has an entrance port aperture havinga diameter of 20 mm for use in the measurement. Thus, a piece having asize of 22 mm×22 mm or larger may be cut out from the optical film asappropriate. If the optical film is small in size, the optical film isgradually shifted or turned in such an extent that the light source spotis within the piece of film to secure three measurement positions. Incases where the optical film is in roll form, the optical film has aneffective portion, which is a portion used for a product (for example,an image display device), and a non-effective portion, which is aportion not used for a product. An optical film piece to be cut formeasurement of a haze value and the like should be cut out from theeffective portion of the optical film. For example, portions 5 cm fromboth ends of the optical film in the width direction can benon-effective portions.

In cases where an additional film, such as polarizing plate, is providedon one surface of the optical film 10 through an adhesive or adhesionlayer, the haze value of the optical film should be measured afterremoving the additional film and the adhesive or adhesion layer. Theadditional film can be removed, for example, as follows. First of all, alaminate consisting of an optical film attached to an additional filmthrough an adhesive or adhesion layer is heated with a hair dryer and isslowly separated by inserting a cutter blade into a possible interfacebetween the optical film and the additional film. By repeating such aprocess of heating and separation, the adhesive or adhesion layer andthe additional film can be removed. Even if such a removal process isperformed, measurement of the haze value is not significantly affected.

The optical film 10 preferably has a total light transmittance of 80% ormore. The optical film 10 having a total light transmittance of 80% ormore can obtain a sufficient light-transmitting property. A total lighttransmittance of 85% or more or 90% or more for the optical film 10 ispreferable increasingly in this order (the larger the value, the morepreferable).

The above-described total light transmittance can be measured using ahaze meter (product name “HM-150”; manufactured by Murakami ColorResearch Laboratory Co., Ltd.) in accordance with JIS K7361-1: 1997. Theabove-described total light transmittance is defined as the arithmeticmean of three haze values, wherein the three haze values are obtained bycutting a piece of 50 mm×100 mm from one optical film and placing thepiece of film without any curl or wrinkle and without any fingerprint ordirt, into the haze meter in such a manner that the inorganic layer sidefaces opposite to the light source to measure the haze value, andrepeating the measurement three times. In the optical film 10, not onlythe surface 10A but also a laminated layer such as the hard coat layer12 is visually observed to be flat and also has a deviation in filmthickness within ±10%. Accordingly, it is considered that an approximateaverage total light transmittance of the whole optical film can beobtained by measuring the total light transmittance at three differentpositions on the piece cut out from the optical film. The deviation intotal light transmittance is within ±10% even if a measurement objecthas a size as large as 1 m×3000 m or has the same size as a 5-inchsmartphone. In cases where an optical film cannot be cut to theabove-described size, a piece having a size of 22 mm×22 mm or larger maybe cut out from the optical film as appropriate. If the optical film issmall in size, the optical film is gradually shifted or turned in suchan extent that the light source spot is within the piece of film tosecure three measurement positions.

In cases where an additional film, such as polarizing plate, is providedon one surface of the optical film 10 through an adhesive or adhesionlayer, the total light transmittance of an optical film should bemeasured after removing the additional film and the adhesive or adhesionlayer in the same manner as described above. Even if such a removalprocess is performed, measurement of the total light transmittance isnot significantly affected.

The optical film 10 preferably has a yellow index (YI) of 15 or less. Incases where the optical film 10 has a yellow index YI of 15 or less, theoptical film is not so noticeably yellow and thus applicable to usesthat require the optical film to be transparent. The upper limit ofyellow index (YI) in the optical film 10 is more preferably 10 or less.The yellow index (YI) is obtained by measuring a cut piece of theoptical film with a size of 50 mm×100 mm using a spectrophotometer(product name “UV-3100PC”; manufactured by Shimadzu Corporation; lightsource: tungsten lamp and deuterium lamp), processing the obtainedvalues according to the formula described in JIS Z8722: 2009 tocalculate color tristimulus values X, Y, and Z, and processing theobtained tristimulus values X, Y, and Z according to a formula describedin ASTM D1925: 1962 to calculate a yellow index. The above-describedyellow index (YI) is the arithmetic mean of three measurements obtainedby measuring a cut piece of the optical film.

In cases where an additional film, such as polarizing plate, is providedon one surface of the optical film 10 through an adhesive or adhesionlayer, the yellow index (YI) should be measured after removing theadditional film and the adhesive or adhesion layer in the same manner asdescribed above. Even if such a removal process is performed,measurement of the yellow index (YI) is not significantly affected.

The yellow index (YI) of the optical film 10 may be adjusted, forexample, by adding a coloring substance of blue color, the complementarycolor to yellow, to the light-transmitting base material 11 or the hardcoat layer 12. Even if use of a base material composed of a polyimideresin as the light-transmitting base material 11 results in a yellowcolor problem, the yellow index (YI) of the optical film 10 can bedecreased by adding a blue coloring substance to the light-transmittingbase material 11 or the hard coat layer 12.

The above-described blue coloring substance may be either a pigment or adye, and preferably has both light and heat resistance in cases where,for example, the optical film 10 is used in an organic light emittingdiode display device. As the above-described blue coloring substance, anorganic pigment such as a polycyclic or metal complex organic pigment isless prone to molecular breakage by ultraviolet light, in contrast tothe tendency to form a molecular dispersion of the dye itself, and has afurther excellent light resistance, and is thus suitable for uses thatrequire an optical film to be, for example, light resistant. Morespecifically, phthalocyanine organic pigments are suitable. However,pigment particles are dispersed in a solvent and the scattered particlescause loss of transparency. Thus, the size of dispersed pigmentparticles is preferably in the Rayleigh scattering region. On the otherhand, in cases where the transparency of an optical film is critical, adye which is molecularly-dispersed in a solvent is preferably used asthe above-described blue coloring substance.

The optical film 10 preferably has a light transmittance of 8% or lessat a wavelength of 380 nm. In cases where the above-describedtransmittance of the optical film is 8% or less and such an optical filmis used in a mobile terminal, a polarizer inside the mobile terminal canbe inhibited from being degraded by exposure to ultraviolet light. Theupper limit of the light transmittance of the optical film 10 is morepreferably 5%. The above-described transmittance can be measured using aspectrophotometer (product name “UV-3100PC”; manufactured by ShimadzuCorporation; light source: tungsten lamp and deuterium lamp). Theabove-described transmittance is the arithmetic mean of threemeasurements obtained by measuring a cut piece of the optical film witha size of 50 mm×100 mm. The above-described transmittance of the opticalfilm 10 can be achieved by adjusting the amount of the below-describedultraviolet absorber added to the hard coat layer 12.

From a foldability viewpoint, no crack or break is formed in the opticalfilm 10 even in cases where the below-described folding test is repeatedon the optical film preferably one hundred thousand times, morepreferably two hundred thousand times, and further preferably onemillion times. In cases where the folding test is repeated on theoptical film 10 one hundred thousand times and the optical film 10 is,for example, cracked, the optical film 10 shows low foldability.

In cases where an additional film, such as polarizing plate, is providedon one surface of the optical film through an adhesive or adhesionlayer, the folding test for the optical film should be carried out afterremoving the additional film and the adhesive or adhesion layer from theoptical film in the same manner as described above. In cases where afolding test is carried out on a laminate having an additional filmattached to the optical film through an adhesive layer or an adhesionlayer, it is preferable that no crack or break is formed in the opticalfilm even after repeating the folding test ten thousand times.

The folding test is carried out as follows. The folding test starts withfixing the edge 10C and opposite edge 10D of the optical film 10 cut toa size of 20 mm×100 mm to fixing members 20 arranged in parallel to eachother, as shown in FIG. 3(A). In cases where an optical film cannot becut to the above-described size, a piece having a size of 20 mm×40 mm orlarger may be cut out from the optical film as appropriate.Additionally, the fixing members 20 can slide in the horizontaldirection, as shown in FIG. 3(A).

Next, the fixing members 20 are moved close to each other to fold anddeform the optical film 10, as shown in FIG. 3(B); the fixing members 20are further moved until a gap of 6 mm is left between the two opposingedges 10C and 10D of the optical film 10 fixed to the fixing members 20,as shown in FIG. 3(C); subsequently, the fixing members 20 are moved inopposite directions to resolve the deformation of the optical film 10.

As shown in FIG. 3(A) to (C), the fixing members 20 can be moved to foldthe optical film 10. Additionally, a gap of 6 mm can be maintainedbetween the two opposing edges of the optical film 10 by carrying outthe folding test in a manner that prevents the bent part 10E of theoptical film 10 from being forced out beyond the lower edges of thefixing members 20 and controls the fixing members 20 to keep a distanceby means of a spacer or the like when they approach each other closest.In this case, the outer diameter of the bent part 10E is considered as 6mm.

Additionally, it is preferable that no crack or break is formed in theoptical film 10 after folding the optical film with the inorganic layer13 facing inward at an angle of 180 degrees in such a manner that a gapof 2 mm is left between the opposite edges 10C and 10D of the opticalfilm, unfolding the folded optical film, and repeating the process onehundred thousand times. Also in this case, the folding test is carriedout in the same manner as described above except in such a manner that,after the fixing members 20 are further moved until a gap of 2 mm isleft between the two opposing edges 10C and 10D of the optical film 10fixed to the fixing members 20, the fixing members 20 are moved inopposite directions to resolve the deformation of the optical film 10.

In cases where an additional film, such as polarizing plate, is providedon one surface of the optical film 10 through an adhesive or adhesionlayer, the folding test should be carried out after removing theadditional film and the adhesive or adhesion layer in the same manner asdescribed above. Even if such a removal process is performed, thefolding test is not significantly affected.

The surface 10A of the optical film 10 preferably has a hardness (pencilhardness) of 2H or more as measured by the pencil hardness test definedby JIS K5600-5-4: 1999. The pencil hardness test should be carried outas follows: using a pencil hardness testing machine (product name“Pencil Scratch Hardness Tester (electric type)”; manufactured by ToyoSeiki Seisaku-sho, Ltd.), a pencil (product name “uni”; manufactured byMitsubishi Pencil Co., Ltd.) is moved at a speed of 1 mm/second on thesurface of an optical film piece having a cut size of 50 mm×100 mm whilea load of 750 g is applied to the pencil. The grade of the hardestpencil that leaves no scratch on the surface of the optical film duringthe pencil hardness test is determined as the pencil hardness of theoptical film. A plural number of pencils with different hardness areused for the measurement of pencil hardness and the pencil hardness testis repeated five times on each pencil. In cases where no scratch is madeon the surface of the optical film with a pencil with specific hardnessin four or more out of the five replicates, the pencil with the hardnessis determined to make no scratch on the surface of the optical film. Theabove-described scratch refers to a scratch which is visibly detectablewhen the surface of an optical film subjected to the pencil hardnesstest is observed under transmitting fluorescent light. The pencilhardness of the surface 10A of the optical film 10 is preferably 3H orharder, more preferably 5H, and most preferably 6H or harder.

Light emitting diodes are actively employed in recent years as thebacklight source for image display devices such as personal computersand tablet terminals and such light emitting diodes strongly emit lightcalled blue light. The blue light has a wavelength of 380 to 495 nm andother properties similar to those of ultraviolet light, and the energyof the blue light is so high that the blue light not absorbed by thecornea and the crystalline lens and passing into the retina isconsidered as a cause of retinal damage, eye strain, sleep disorder, andthe like. Thus, an optical film used in an image display device ispreferred to have no influence on the color representation on a displayscreen and to have an excellent blue light blocking property. Therefore,the optical film 10 is preferred to have a spectral transmittance ofless than 1% at a wavelength of 380 nm, a spectral transmittance of lessthan 10% at a wavelength of 410 nm, and a spectral transmittance of 70%or more at a wavelength of 440 nm in view of blue light blocking effectbecause the above-described optical film having a spectral transmittanceof 1% or more at a wavelength of 380 nm or a spectral transmittance of10% or more at a wavelength of 410 nm may not solve blue light problemsand the optical film having a spectral transmittance of less than 70% ata wavelength of 440 nm may give some effects on the color representationon the display screen of an image display device in which the opticalfilm is used. In the blue light wavelength range, the optical film 10can sufficiently absorb light having a wavelength of 410 nm or less andsufficiently pass light having a wavelength of 440 nm or more, and canexhibit excellent blue light blocking performance without affecting thecolor representation on a display screen. Additionally, use of theoptical film 10 with such an excellent blue light blocking property inan organic light emitting diode (OLED) display device as an imagedisplay device effectively inhibits degradation of the organic lightemitting diode device.

Preferably, the optical film 10 has a transmittance of nearly 0% forlight with a wavelength of up to 380 nm, gradually increases the lighttransmittance above a wavelength of 410 nm, and exhibits a sharpincrease of light transmittance around a wavelength 440 nm.Specifically, the spectral transmittance of the optical film preferablyvaries sigmoidally with the wavelength, for example, from 410 nm to 440nm. The above-described optical film has: more preferably a spectraltransmittance of less than 0.5%, further preferably less than 0.2%, at awavelength of 380 nm; more preferably a spectral transmittance of lessthan 7%, more preferably less than 5%, at a wavelength of 410 nm; andmore preferably a spectral transmittance of 75% or more, furtherpreferably 80% or more, at a wavelength of 440 nm. The optical film 10preferably has a spectral transmittance of less than 50% at a wavelength420 nm. The optical film 10 fulfilling such requirements with respect tospectral transmittance exhibits a sharp increase of transmittance arounda wavelength of 440 nm and can obtain a very excellent bluelight-blocking property without affecting the color representation on adisplay screen.

The optical film 10 has: more preferably a spectral transmittance ofless than 0.1% at a wavelength of 380 nm; more preferably a spectraltransmittance of less than 7% at a wavelength of 410 nm; and morepreferably a spectral transmittance of 80% or more at a wavelength of440 nm.

The slope as a function of wavelength obtained by the least squaremethod applied to the transmittance of the optical film 10 is preferablymore than 2.0 in a spectrum range from 415 to 435 nm. In cases where theabove-described slope is 2.0 or less, the optical film fails to cut asufficient amount of light in the blue light wavelength range, such as awavelength range from 415 to 435 nm, and may exhibit an attenuated bluelight-cutting function. Also, the optical film may cut an excess amountof light in the blue light wavelength range (wavelengths from 415 to 435nm) and, in that case, interferes with the backlight or the light in awavelength range emitted from an image display device (for example,light with wavelengths equal to and above 430 nm emitted from an OLED)and be highly likely to cause a problem such as poor colorrepresentation. The above-described slope can be calculated, forexample, by measuring at least five points spaced 1 nm apart to obtainthe transmittance data in a range from 415 to 435 nm using aspectrophotometer with the ability to permit measurement to 0.5 nmaccuracy (product name “UV-3100PC”; manufactured by ShimadzuCorporation).

The optical film 10 preferably has a blue light blocking rate of 40% ormore. In cases where the blue light blocking rate is less than 40%, theabove-described blue light problems may not be sufficiently resolved.The above-described blue light blocking rate is calculated according to,for example, JIS T7333: 2005. Such a blue light blocking rate can beeffected, for example, by adding the below-described sesamol typebenzotriazole monomer to the hard coat layer 12.

Examples of applications of the optical film 10 include, but are notparticularly limited to, image display devices in smartphones, tabletterminals, personal computers (PCs), wearable terminals, digital signagesystems, televisions, automotive navigation systems, and the like.Additionally, the optical film 10 is also suitable for vehicle displays.The form of each above-described image display device is also favorablefor applications which require flexible forms, such as foldable orrollable forms.

The optical film 10 can be cut into a desired size or may be rolled. Incases where the optical film 10 is cut into a desired size, the opticalfilm is not limited to a particular size, and the size of the film isappropriately determined depending on the display size of an imagedisplay device. Specifically, the optical film 10 may be, for example,2.8 inches or more and 500 inches or less in size. The term “inch” asused herein shall refer to the length of a diagonal when the opticalfilm is rectangular, and to the length of a diameter when the opticalfilm is circular, and to the average of major and minor axes when theoptical film is elliptical. In this respect, if the optical film isrectangular, the aspect ratio of the optical film is not limited to aparticular ratio when the above-described size in inch is determined, aslong as no problem is found with the optical film used for the displayscreen of an image display device. Examples of the aspect ratio includeheight-to-width ratios of 1:1, 4:3, 16:10, 16:9, and 2:1. However,particularly in optical films used for vehicle displays and digitalsignage systems which are rich in designs, the aspect ratio is notlimited to the above-described aspect ratios. Additionally, in caseswhere the optical film 10 is large in size, the optical film will be cutto the A5 size (148 mm×210 mm) starting at an arbitrary position andthen cut to fit size requirements of each measurement item.

In an image display device, the optical film 10 may be installed insidethe image display device, and is preferably installed near the surfaceof the image display device. In cases of being installed near thesurface of an image display device, the optical film 10 serves as acover film, which is used instead of a cover glass.

<<Light-Transmitting Base Material>>

The light-transmitting base material 11 is a base material having alight transmitting property. The term “light-transmitting” as usedherein refers to a property that allows light transmission, including,for example, a total light transmittance of 50% or more, preferably 70%or more, more preferably 80% or more, and particularly preferably 90% ormore. The term “light-transmitting” does not necessarily refer totransparency and may refer to translucency.

The thickness of the light-transmitting base material 11 is preferably10 μm or more and 100 μm or less. In cases where the thickness of thelight-transmitting base material is 10 μm or more, the resulting opticalfilm 10 can be inhibited from curling and also has such sufficienthardness that the pencil hardness is enabled to be 3H or harder.Furthermore, such an optical film produced by roll-to-roll process canbe inhibited from forming wrinkles, and thus eliminates the fear ofhaving a deteriorated appearance. In cases where the thickness of thelight-transmitting base material 11 is 100 μm or less, the resultingoptical film has sufficient foldability and is desirable in terms ofweight saving. The thickness of the light-transmitting base material isdefined as the arithmetic mean of thickness values measured at 10different locations, where a cross-section of the light-transmittingbase material is photographed using a scanning electron microscope (SEM)and the thickness of the light-transmitting base material is measured atthe 10 locations within the image of the cross-section. The lower limitof the light-transmitting base material 11 is more preferably 25 μm ormore in thickness, while the upper limit of the light-transmitting basematerial 11 is more preferably 80 μm or less in thickness.

Examples of the constituent material for the light-transmitting basematerial 11 include resins such as polyimide resins, polyamide-imideresins, polyamide resins, polyester resins (for example, polyethyleneterephthalate and polyethylene naphthalate). Among those resins,polyimide resins, polyamide resins, and combinations thereof arepreferred in terms of several criteria: the resulting optical film hasexcellent hardness and transparency as well as is less cracked or brokenduring the folding test, and also has such an outstanding heatresistance that the optical film can obtain further excellent hardnessand transparency by film baking.

A polyimide resin can be obtained from the reaction between atetracarboxylic component and a diamine component. The polyimide resinis not limited to a particular one and preferably has, for example, atleast one structure selected from the group consisting of the structuresrepresented by the general formula (1) below and the general formula (3)below, in terms of having an excellent light transmitting property andexcellent rigidity.

In the above-described general formula (1), R¹ represents atetracarboxylic acid residue as a tetravalent group; R² represents atleast one divalent group selected from the group consisting oftrans-cyclohexanediamine residue, trans-1,4-bismethylenecyclohexanediamine residue, 4,4′-diaminodiphenyl sulfone residue,3,4′-diaminodiphenyl sulfone residue, and divalent groups represented bythe general formula (2) below; n represents the number of repeatingunits, which is 1 or more. In this specification, the “tetracarboxylicacid residue” refers to a residue remaining after subtracting fourcarboxylic groups from a tetracarboxylic acid, and represents the samestructure as a residue remaining after subtracting the acid dianhydridestructure from a tetracarboxylic dianhydride. Additionally, the “diamineresidue” refers to a residue remaining after subtracting two aminogroups from a diamine.

In the above-described general formula (2), R³ and R⁴ each independentlyrepresent a hydrogen atom, alkyl group, or perfluoroalkyl group.

In the above-described general formula (3), R⁵ represents at least onetetravalent group selected from the group consisting of cyclohexanetetracarboxylic acid residue, cyclopentane tetracarboxylic acid residue,dicyclohexane-3,4,3′,4′-tetracarboxylic acid residue, and4,4′-(hexafluoroisopropylidene)diphthalic acid residue; R⁶ represents adiamine residue as a divalent group; and n′ represents the number ofrepeating units, which is 1 or more.

In the above-described general formula (1), R¹ refers to atetracarboxylic acid residue and can represent, as indicated above, aresidue remaining after subtracting the acid dianhydride structure froma tetracarboxylic dianhydride. As R¹ in the above-described generalformula (1), at least one selected from the group consisting of4,4′-(hexafluoroisopropylidene)diphthalic acid residue,3,3′,4,4′-biphenyl tetracarboxylic acid residue, pyromellitic residue,2,3′,3,4′-biphenyl tetracarboxylic acid residue, 3,3′,4,4′-benzophenonetetracarboxylic acid residue, 3,3′,4,4′-diphenylsulfone tetracarboxylicacid residue, 4,4′-oxydiphthalic acid residue, cyclohexanetetracarboxylic acid residue, and cyclopentane tetracarboxylic acidresidue is preferably contained, among others, in terms of improving thelight-transmitting property and the rigidity. At least one selected fromthe group consisting of 4,4′-(hexafluoroisopropylidene)diphthalic acidresidue, 4,4′-oxydiphthalic acid residue, and 3,3′,4,4′-diphenylsulfonetetracarboxylic acid residue is further preferably contained.

As R¹, those suitable residues are contained in total preferably at acontent of 50% by mole or more, further preferably 70% by mole or more,and still further preferably 90% by mole or more.

Additionally, a combination of at least one selected from a group oftetracarboxylic acid residues suitable for improving the rigidity (groupA), such as the group consisting of 3,3′,4,4′-biphenyl tetracarboxylicacid residue, 3,3′,4,4′-benzophenone tetracarboxylic acid residue, andpyromellitic residue, and at least one selected from a group oftetracarboxylic acid residues suitable for improving the transparency(group B), such as the group consisting of4,4′-(hexafluoroisopropylidene)diphthalic acid residue,2,3′,3,4′-biphenyl tetracarboxylic acid residue,3,3′,4,4′-diphenylsulfone tetracarboxylic acid residue,4,4′-oxydiphthalic acid residue, cyclohexane tetracarboxylic acidresidue, and cyclopentane tetracarboxylic acid residue, is preferablyused as R¹.

For the content ratio of the group of tetracarboxylic acid residuessuitable for improving the rigidity (group A) to the group oftetracarboxylic acid residues suitable for improving the transparency(group B) in that case, preferably 0.05 moles or more and 9 moles orless, further preferably 0.1 moles or more and 5 moles or less, stillfurther preferably 0.3 moles or more and 4 moles or less, of the groupof tetracarboxylic acid residues suitable for improving the rigidity(group A) are combined with 1 mole of the group of tetracarboxylic acidresidues suitable for improving the transparency (group B).

In the above-described general formula (1), R² preferably represents atleast one divalent group selected from the group consisting of4,4′-diaminodiphenyl sulfone residue, 3,4′-diaminodiphenyl sulfoneresidue, and divalent groups represented by the above-described generalformula (2), further preferably at least one divalent group selectedfrom the group consisting of 4,4′-diaminodiphenyl sulfone residue,3,4′-diaminodiphenyl sulfone residue, and divalent groups represented bythe above-described general formula (2) where R3 and R4 each represent aperfluoroalkyl group, among others, in terms of improving thelight-transmitting property and the rigidity.

As R⁵ in the above-described general formula (3),4,4′-(hexafluoroisopropylidene)diphthalic acid residue,3,3′,4,4′-diphenylsulfone tetracarboxylic acid residue, andoxydiphthalic acid residue are preferably contained, among others, interms of improving the light transmitting property and the rigidity.

As R⁵, those suitable residues are contained preferably at a content of50% by mole or more, further preferably 70% by mole or more, and stillfurther preferably 90% by mole or more.

In the above-described general formula (3), R⁶ refers to a diamineresidue and can represent, as indicated above, a residue remaining aftersubtracting two amino groups from a diamine. As R⁶ in theabove-described general formula (3), preferably at least one divalentgroup selected from the group consisting of2,2′-bis(trifluoromethyl)benzidine residue,bis[4-(4-aminophenoxy)phenyl]sulfone residue, 4,4′-diaminodiphenylsulfone residue, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropaneresidue, bis[4-(3-aminophenoxy)phenyl]sulfone residue,4,4′-diamino-2,2′-bis(trifluoromethyl)diphenyl ether residue,1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene residue,2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropaneresidue, 4,4′-diamino-2-(trifluoromethyl)diphenyl ether residue,4,4′-diaminobenzanilide residue, N,N′-bis(4-aminophenyl)terephthalamideresidue, and 9,9-bis(4-aminophenyl)fluorene residue, further preferablyat least one divalent group selected from the group consisting of2,2′-bis(trifluoromethyl)benzidine residue,bis[4-(4-aminophenoxy)phenyl]sulfone residue, and 4,4′-diaminodiphenylsulfone residue, is contained, among others, in terms of improving thelight transmitting property and the rigidity.

As R⁶, those suitable residues are contained in total preferably at acontent of 50% by mole or more, further preferably 70% by mole or more,and still further preferably 90% by mole or more.

Additionally, a combination of at least one selected from a group ofdiamine residues suitable for improving the rigidity (group C), such asthe group consisting of bis[4-(4-aminophenoxy)phenyl]sulfone residue,4,4′-diaminobenzanilide residue, N,N′-bis(4-aminophenyl)terephthalamideresidue, paraphenylenediamine residue, methaphenylenediamine residue,and 4,4′-diaminodiphenylmethane residue, and at least one selected froma group of diamine residues suitable for improving the transparency(group D), such as the group consisting of2,2′-bis(trifluoromethyl)benzidine residue, 4,4′-diaminodiphenyl sulfoneresidue, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane residue,bis[4-(3-aminophenoxy)phenyl]sulfone residue,4,4′-diamino-2,2′-bis(trifluoromethyl)diphenyl ether residue,1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene residue,2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropaneresidue, 4,4′-diamino-2-(trifluoromethyl)diphenyl ether residue, and9,9-bis(4-aminophenyl)fluorene residue, is preferably used as R⁶.

For the content ratio of the group of diamine residues suitable forimproving the rigidity (group C) to the group of diamine residuessuitable for improving the transparency (group D) in that case,preferably 0.05 moles or more and 9 moles or less, further preferably0.1 moles or more and 5 moles or less, more preferably 0.3 moles or moreand 4 moles or less, of the group of diamine residues suitable forimproving the rigidity (group C) are combined with 1 mole of the groupof diamine residues suitable for improving the transparency (group D).

For the structures represented by the above-described general formulae(1) and (3), n and n′ each independently represent the number ofrepeating units, which is 1 or more. The number of repeating units, n,in the polyimide may be appropriately selected depending on thestructure to allow the polyimide to have a preferred glass transitiontemperature as described below, and is not limited to a particularnumber. The average number of repeating units is typically 10 to 2,000,further preferably 15 to 1,000.

Additionally, the polyimide resin may partially contain a polyamidestructure. Examples of the polyamide structure that may be containedinclude a polyamide-imide structure containing a tricarboxylic acidresidue such as trimellitic anhydride, and a polyamide structurecontaining a dicarboxylic acid residue such as terephthalic acid.

The polyimide resin preferably has a glass transition temperature of250° C. or higher, further preferably 270° C. or higher, in terms ofheat resistance, while the polyimide resin preferably has a glasstransition temperature of 400° C. or lower, further preferably 380° C.or lower, in terms of ease of stretching and of reducing the bakingtemperature.

Specific examples of the polyimide resin include compounds having thestructure represented by the formula below. In the formula below, nrepresents the number of repeating units, which is an integer of 2 ormore.

Among the above-described polyimide resins, the polyimide or polyamideresins having structures that inhibit intramolecular or intermolecularcharge transfer are preferred due to the excellent transparency,specifically including the fluorinated polyimide resins represented by,for example, the above-described formulae (4) to (11) and the polyimideresins containing alicyclic structures represented by, for example, theabove-described formulae (13) to (16).

Additionally, the fluorinated polyimide resins represented by, forexample, the above-described formulae (4) to (11) each contain afluorinated structure and thus have a high heat resistance, whichprotects a polyimide film composed of any of the polyimide resins fromcoloration by the heat generated during the synthesis of the polyimideresin and helps the polyimide resin to maintain excellent transparency.

The concept of polyamide resin includes aromatic polyamides (aramids) aswell as aliphatic polyamides. The polyamide resin generally refers to aresin having the backbone represented by the formula (21) or (22) below,and examples of the above-described polyamide resin include a compoundrepresented by the formula (23) below. In the formula below, nrepresents the number of repeating units, which is an integer of 2 ormore.

A commercially available base material may be used as a base materialcomposed of the polyimide or polyamide resin represented by any of theabove-described formulae (4) to (20) and (23). Examples of acommercially available base material composed of the above-describedpolyimide resin include Neopulim and the like manufactured by MitsubishiGas Chemical Company, Inc., while examples of a commercially availablebase material composed of the above-described polyamide resin includeMictron and the like manufactured by Toray Industries, Inc.

Additionally, a base material synthesized by a known method may be usedas a base material composed of the polyimide or polyamide resinrepresented by any of the above-described formulae (4) to (20) and (23).For example, the polyimide resin represented by the above-describedformula (4) is synthesized by a method described JP2009-132091A and canbe obtained, specifically, by a reaction of4,4′-hexafluoropropylidenebisphthalic dianhydride (FPA) and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB), as represented bythe formula (24) below.

The weight average molecular weight of the above-described polyimide orpolyamide resin preferably ranges from 3,000 to 500,000 inclusive, morepreferably from 5,000 to 300,000, and further preferably from 10,000 to200,000 inclusive. In cases where the weight average molecular weight isless than 3,000, the resin may not have enough strength; in cases wherethe weight average molecular weight is more than 500,000, the resin hasan increased viscosity and a reduced solubility, which in turn mayresult in failure to provide a base material with smooth surface andhomogeneous film thickness. In this specification, the “weight averagemolecular weight” is measured by gel permeation chromatography (GPC) asa value in terms of polystyrene.

Among the above-described polyimide and polyamide resins, the polyimideor polyamide resins having structures that inhibit intramolecular orintermolecular charge transfer are preferred due to the excellenttransparency, specifically including the fluorinated polyimide resinsrepresented by, for example, the above-described formulae (4) to (11),the polyimide resins containing alicyclic structures represented by, forexample, the above-described formulae (13) to (16), and the halogenatedpolyamide resin represented by, for example, the above-described formula(23).

Additionally, the fluorinated polyimide resins represented by, forexample, the above-described formulae (4) to (11) each contain afluorinated structure and thus have a high heat resistance, whichprotects a base material composed of any of the polyimide resins fromcoloration by the heat generated during the synthesis of the polyimideresin and helps the polyimide resin to maintain excellent transparency.

As the light-transmitting base material 11, a base material composed ofthe fluorinated polyimide resin represented by, for example, any of theabove-described formulae (4) to (11) or composed of the halogenatedpolyamide resin represented by, for example, the above-described formula(23) is preferably used because use of such a base material allows theresulting optical film to have a hardness of 3H or harder when measuredunder the same conditions of the pencil hardness test specified by JISK5600-5-4: 1999 as those used for the surface 13A of the inorganic layer13 (load: 1 kg, speed: 1 mm/second). Among those base materials, a basematerial composed of the polyimide resin represented by theabove-described formula (4) is more preferably used because use of thebase material can provide very excellent hardness with a pencil hardnessof 3H or harder as described above to the resulting optical film.

Examples of the polyester resin include resins containing at least oneof polyethylene terephthalate, polypropylene terephthalate, polybutyleneterephthalate, and polyethylene naphthalate as a component.

<<Hard Coat Layer>>

The hard coat layer 12 has an indentation hardness (H_(IT)) of 200 MPaor more. As used herein, “indentation hardness” refers to a valuedetermined from a load-displacement curve obtained in hardnessmeasurement by a nanoindentation method and drawn from the loading tounloading of an indenter. As the lower limit of the indentation hardness(H_(IT)) of the hard coat layer 12, 200 MPa or more, 500 MPa or more, or800 MPa or more is preferable in this order (the larger the value, themore preferable). As the upper limit of the indentation hardness of thehard coat layer 12, 1500 MPa or less, 1300 MPa or less, or 1100 MPa orless is preferable in this order (the smaller the value, the morepreferable) in terms of inhibiting the hard coat layer 12 fromgenerating breaks or cracks when the optical film 10 is folded.

Measurement of the indentation hardness (H_(IT)) should be performed ona measurement sample using a “TI950 TriboIndenter” manufactured byHysitron, Inc. Specifically, a piece having a size of 1 mm×10 mm is cutout from the optical film and embedded in an embedding resin to preparea block, and homogeneous sections having a thickness of 70 nm or moreand 100 nm or less and having no openings or the like are cut out fromthe block according to a commonly used sectioning technique. For thepreparation of sections, an “Ultramicrotome EM UC7” (Leica MicrosystemsGmbH) or the like can be used. Then, the block remaining after cuttingout the homogeneous sections having no openings or the like is used as ameasurement sample. Subsequently, a Berkovich indenter (a trigonalpyramid, TI-0039, manufactured by BRUKER Corporation) as theabove-described indenter is pressed perpendicularly into thecross-section of the hard coat layer in the cross-section of themeasurement sample obtained after cutting out the sections, wherein theindenter is pressed up to the maximum pressing load of 500 μN over 25seconds under the below-mentioned measurement conditions. Here, aBerkovich indenter should be pressed into a part of the hard coat layerin order to avoid the influence of the light-transmitting base materialand the inorganic layer and avoid the influence of the side edges of thehard coat layer, wherein the part is 500 nm away into the central sideof the hard coat layer from the interface between the light-transmittingbase material and the hard coat layer, 500 nm away into the central sideof the hard coat layer from the interface between the hard coat layerand the inorganic layer, and 500 nm away into the central side of thehard coat layer from both side edges of the hard coat layer. In caseswhere a functional layer is present between the light-transmitting basematerial and the hard coat layer, the Berkovich indenter should bepressed into a part of the hard coat layer, wherein the part is 500 nmaway into the central side of the hard coat layer from the interfacebetween the functional layer and the hard coat layer, 500 nm away intothe central side of the hard coat layer from the interface between thehard coat layer and the inorganic layer, and 500 nm away into thecentral side of the hard coat layer from both side edges of the hardcoat layer. Subsequently, the intender is held at the position for acertain period of time to relax the residual stress, and then unloadedover 25 seconds to measure the maximum load after the relaxation, andthe maximum load P_(max) (μN) and the contact projection area A_(p)(nm²) are used to calculate an indentation hardness (H_(IT)) from thevalue of P_(max)/A_(p). The contact projection area is a contactprojection area, for which the tip curvature of the indenter iscorrected using fused quartz (5-0098, manufactured by BRUKERCorporation) as a standard sample in accordance with the Oliver-Pharrmethod. The arithmetic mean of the measurements at 10 differentlocations is determined as the indentation hardness (H_(IT)). In caseswhere the measurement values include a value deviating ±20% or more fromthe arithmetic mean value, the deviating value should be excluded,followed by remeasurement. Whether the measurement values include avalue deviating ±20% or more from the arithmetic mean value should bedetermined on the basis of whether a value (%) calculated from(A−B)/B×100 is ±20% or more, wherein A is a measurement value, and B isthe arithmetic mean value. The indentation hardness (H_(IT)) can beadjusted by selecting the kind of the binder resin 12A, the amount ofthe inorganic particles 12B, and the like as below mentioned.

(Measurement conditions)

-   -   loading speed: 20 μN/second;    -   retention time: 5 seconds;    -   unloading speed: 20 μN/second;    -   measurement temperature: 25° C.

The hard coat layer 12 has a film thickness of 1 μm or more. The hardcoat layer 12 having a film thickness of 1 μm or more allows steel woolto fall in to a smaller degree in a steel wool test, and thus makes itpossible to inhibit the surface of the hard coat layer from beingscratched. As the lower limit for the hard coat layer 12, 2 μm or more,3 μm or more, or 4 μm or more is preferable in this order (the largerthe value, the more preferable). As the upper limit for the hard coatlayer 12, 10 μm or less, 9 μm or less, 8 μm or less, or 7 μm or less ispreferable in this order (the smaller the value, the more preferable) interms of obtaining sufficient foldability.

The film thickness of the hard coat layer is defined as the arithmeticmean of film thickness values measured at 10 different locations, wherea cross-section of the hard coat layer is photographed using a scanningtransmission electron microscope (STEM) or a transmission electronmicroscope (TEM), and the film thickness of the hard coat layer ismeasured at the 10 locations within the image of the cross-section. Aspecific method of acquiring cross-sectional images is described below.First of all, a piece of 1 mm×10 mm cut out from an optical film isembedded in an embedding resin to prepare a block, and homogeneoussections having a thickness of 70 nm or more and 100 nm or less andhaving no openings or the like are cut out from the block according to acommonly used sectioning technique. For the preparation of sections, an“Ultramicrotome EM UC7” (Leica Microsystems GmbH) or the like can beused. Then, these homogeneous sections having no openings or the likeare used as measurement samples. Subsequently, cross-sectional images ofthe measurement sample are acquired using a scanning transmissionelectron microscope (STEM) (product name “S-4800”; manufactured byHitachi High-Technologies Corporation). The cross-sectional images areacquired using the above-described S-4800 by setting the detector to“TE,” the accelerating voltage to “30 kV,” and the emission current to“10 μA.” The focus, contrast, and brightness are appropriately adjustedat a magnification of 5000 to 200,000 times, so that each layer can beidentified by observation. The magnification is preferably 10,000 timesto 100,000 times, more preferably 10,000 times to 50,000 times, mostpreferably 25,000 times to 50,000 times. Furthermore, the beam monitoraperture, the objective lens aperture, and the WD may be respectivelyset to “3,” “3,” and “8 mm,” in acquirement of cross-sectional imagesusing the above-described S-4800. For the measurement of the filmthickness of the hard coat layer, it is important that the contrast atthe interfacial boundary between the hard coat layer and another layer(for example, the functional layer) can be observed as clearly aspossible when the cross-section is observed. In cases where theinterfacial boundary is hardly observed due to lack of contrast, astaining process may be applied because interfacial boundaries betweenorganic layers become easily observed by application of a stainingprocedure with osmium tetraoxide, ruthenium tetraoxide, phosphotungsticacid, or the like. Additionally, higher magnification may make it moredifficult to find the interfacial contrast. In that case, theobservation is also carried out with low magnification. For example, theobservation is carried out with two magnifications consisting of ahigher magnification and a lower magnification, such as 25,000 and50,000 times, or 50,000 and 100,000 times, to determine the abovearithmetic means at both magnifications, which are further averaged todetermine the film thickness of the hard coat layer.

The hard coat layer 12 contains a binder resin 12A and inorganicparticles 12B. The hard coat layer 12 may contain an additive such as anultraviolet absorber or a spectral transmittance modifier in addition tothe binder resin 12A and the inorganic particles 12B.

The inorganic particles 12 B preferably have an area ratio of 5% or moreand 75% or less in the region IR (hereinafter may be referred to as an“interfacial region”) up to a depth of 500 nm into the hard coat layer12 shown in FIG. 2 from the interface IF between the hard coat layer 12and the inorganic layer 13 in the cross-section of the hard coat layer12 in the film thickness direction. The inorganic particles having anarea ratio of 5% or more in the interfacial region IF mean that the hardcoat layer 12 contains the inorganic particles 12B in a large amount,and thus can make the hard coat layer 12 harder and enhance theadhesiveness to the inorganic layer 13. A steel wool test is carried outwith a load applied onto the surface of the inorganic layer, and theload is applied onto the inorganic layer not only in the film thicknessdirection but also in the shear direction so that the steel wool can rubthe surface of the inorganic layer. The inorganic particles 12B havingan area ratio of 75% or less in the interfacial region IR are lesslikely to cause scratches and chips even when a load is applied in theshear direction in a steel wool test, because the binder resin 12A ispresent to some extent in the hard coat layer 12. Additionally, thebinder resin 12A present to some extent in the hard coat layer 12 alsomakes it possible to further enhance the adhesiveness to the functionallayer 14. Here, the area ratio of the inorganic region in theinterfacial region is determined because the interfacial region is aregion which is particularly susceptible to scratching and chipping whena steel wool test is carried out. As the lower limit of the area ratioof the inorganic particles 12B in the interfacial region IF, 23% ormore, 33% or more, or 44% or more is preferable in this order (thelarger the value, the more preferable). As the upper limit of the arearatio of the inorganic particles 12B in the interfacial region IF, 71%or less, 67% or less, or 60% or less is preferable in this order (thesmaller the value, the more preferable).

The area ratio of the inorganic particles in the interfacial regionshould be determined as below-mentioned. First of all, a piece of 1mm×10 mm cut out from an optical film is embedded in an embedding resinto prepare a block, and 10 homogeneous sections having a thickness of 70nm or more and 100 nm or less and having no openings or the like are cutout from the block according to a commonly used sectioning technique.For the preparation of sections, an “Ultramicrotome EM UC7” (LeicaMicrosystems GmbH) or the like can be used. Then, these 10 homogeneoussections having no openings or the like are used as measurement samples.Then, a cross-sectional image of each measurement sample is acquiredusing a transmission electron microscope (TEM) or a scanningtransmission electron microscope (STEM). Here, the cross-sectional imageof one part per measurement sample should be acquired. In cases wherethe cross-sectional image of each measurement sample is acquired using ascanning transmission electron microscope (STEM) (product name “S-4800”;manufactured by Hitachi High-Technologies Corporation), thiscross-sectional image is acquired by setting the detector to “TE,” theaccelerating voltage to “30 kV,” and the emission current to “10 μA.”The focus, contrast, and brightness are appropriately adjusted at amagnification of 5000 to 200,000 times, so that each layer can beidentified by observation. The magnification is preferably 10,000 timesto 100,000 times, more preferably 10,000 times to 50,000 times, mostpreferably 25,000 times to 50,000 times. Furthermore, the beam monitoraperture, the objective lens aperture, and the WD may be respectivelyset to “3,” “3,” and “8 mm,” in acquirement of cross-sectional images.Assuming that the area of the interfacial region is 100% in each of theobtained 10 cross-sectional images, the ratio (area ratio) of the areaof the inorganic particles to the area of the interfacial region isdetermined. The area ratio of the inorganic particles in the interfacialregion is the arithmetic mean value of the area ratios of the inorganicparticles determined from the 10 cross-sectional images of theinterfacial region. To obtain such an area ratio of the inorganicparticles 12B, the inorganic particles 12B are preferably contained, forexample, at a ratio (weight ratio) of 10% or more and 300% or less,preferably 10% or more to 200%, relative to a polymerizable compoundcured to become the binder resin 12A.

The inorganic layer 13 side of the hard coat layer 12 may be treated toexpose the inorganic particles 12B by a method of etching the binderresin 12A selectively or another method. Carrying out such a treatmentcan further enhance adhesiveness between the hard coat layer 12 and theinorganic layer 13. However, carrying out this treatment to an excessivedegree causes the inorganic layer side of the hard coat layer to berough, and the small film thickness of the inorganic layer causes thesurface figure of the hard coat layer to be transferred to the surfacefigure of the inorganic layer, with the result that, when a steel wooltest is carried out, the rough figure of the surface of the inorganiclayer catches steel wool, and thus, will undesirably cause a decrease inscratch resistance. Examples of methods of etching the binder resinselectively include glow discharge treatment, plasma treatment, ionetching treatment, and alkali treatment.

<Binder Resin>

The binder resin 12A contains at least one of a polymerized product (acured product) of a polymerizable compound (a curable compound) and athermoplastic resin. The polymerizable compound refers to a moleculehaving at least one of radical polymerizable functional groups andcationic polymerizable functional groups. Hereinafter, a polymerizablecompound having a radical polymerizable functional group is referred toas a radical polymerizable compound, and a polymerizable compound havinga cationic polymerizable functional group referred to as a cationicpolymerizable compound. Examples of radical polymerizable functionalgroups include ethylenic unsaturated groups such as a (meth)acryloylgroup, vinyl group, and allyl group. Both “acryloyl group” and“methacryloyl group” are meant by the word “(meth)acryloyl group.”Examples of cationic polymerizable functional groups include a hydroxylgroup, carboxyl group, isocyanate group, amino group, cyclic ethergroup, mercapto group, and the like.

The binder resin 12A preferably contains less than 10% by mass of apolymerizable compound having a polymerizable functional groupequivalent amount (weight average molecular weight/number ofpolymerizable functional groups) of 130 or more. Containing less than10% by mass of such a polymerizable compound can impart hardness to thehard coat layer 12, and thus, allows the surface 10A of the optical film10 to be less susceptible to scratching and chipping even when subjectedto a steel wool test. Thus, the adhesiveness between the hard coat layer12 and the functional layer 14 can also be enhanced.

The radical polymerizable compound is preferably a polyfunctional(meth)acrylate. Examples of the above-described polyfunctional(meth)acrylate include trimethylolpropane tri(meth)acrylate,tripropylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, dipropylene glycol di(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate,neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, dipentaerythritolpenta(meth)acrylate, tripentaerythritol octa(meth)acrylate,tetrapentaerythritol deca(meth)acrylate, isocyanuric acidtri(meth)acrylate, isocyanuric acid di(meth)acrylate, polyestertri(meth)acrylate, polyesterdi(meth)acrylate, bisphenoldi(meth)acrylate, diglycerol tetra(meth)acrylate, adamantyldi(meth)acrylate, isobornyl di(meth)acrylate, dicyclopentanedi(meth)acrylate, tricyclodecane di(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, and those compounds modified with PO, EO,caprolactone, or the like.

Among those polymerizable compounds, trifunctional to hexafunctionalpolymerizable compounds, such as pentaerythritol triacrylate (PETA),dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate(PETTA), dipentaerythritol pentaacrylate (DPPA), trimethylolpropanetri(meth)acrylate, tripentaerythritol octa(meth)acrylate, andtetrapentaerythritol deca(meth)acrylate, are preferred in terms of theability to achieve the above-described indentation hardness in asuitable manner. In this specification, the word “(meth)acrylate” meansacrylate and methacrylate.

The polymerizable compound may further contain a monofunctional(meth)acrylate monomer for the purpose of, for example, adjusting thehardness of the resin and the viscosity of the composition, andimproving the adhesiveness of the resin. Examples of the above-describedmonofunctional (meth)acrylate monomer include hydroxyethyl acrylate(HEA), glycidyl methacrylate, methoxypolyethylene glycol (meth)acrylate,isostearyl (meth)acrylate, 2-acryloyloxyethyl succinate, acryloylmorpholine, N-acryloyloxyethyl hexahydrophthalimide, cyclohexylacrylate, tetrahydrofuryl acrylate, isobornyl acrylate, phenoxyethylacrylate, and adamantyl acrylate.

The weight average molecular weight of the above-described monomer ispreferably less than 1,000, more preferably 200 or more and 800 or less,in terms of improving the hardness of the hard coat layer 12.Additionally, the weight average molecular weight of the above-describedpolymerizable oligomer is preferably 1,000 or more and 20,000 or less,more preferably 1,000 or more and 10,000 or less, and further preferably2,000 or more and 7,000 or less.

Examples of cationic polymerizable compounds include, but are notparticularly limited to, epoxy compounds, polyol compounds, isocyanatecompounds, melamine compounds, urea compounds, phenol compounds, and thelike.

Examples of thermoplastic resins include styrenic resins, (meth)acrylicresins, vinyl acetate resins, vinyl ether resins, halogen-containingresins, alicyclic olefinic resins, polycarbonate resins, polyesterresins, polyamide resins, cellulose derivatives, silicone resins,rubbers or elastomers, and the like.

<Inorganic Particles>

The inorganic particles 12B are particles composed mainly of aninorganic substance. The inorganic particles 12B may contain an organiccomponent, but are preferably composed only of an inorganic substance.The inorganic particles 12B may be surface-treated with an organiccomponent. The inorganic particles 12B are not limited to a particulartype of inorganic particles as long as those inorganic particles canimprove the hardness, and silica particles are preferred in terms of theability to achieve excellent hardness.

Among silica particles, reactive silica particles are preferred. Theabove-described reactive silica particle can form a cross-linkedstructure with the above-described polyfunctional (meth)acrylate and thepresence of the reactive silica particles can sufficiently increase thehardness of the hard coat layer.

The above-described reactive silica particle preferably has a reactivefunctional group on the surface, and a polymerizable functional group,such as those described above, is suitably used as the reactivefunctional group.

The above-described reactive silica particles are not limited to aparticular type of reactive silica particles, and conventionally knownreactive silica particles, such as reactive silica particles describedin JP2008-165040A, can be used. Additionally, examples of commerciallyavailable reactive silica particles as describe above include MIBK-SD,MIBK-SDMS, MIBK-SDL, and MIBK-SDZL manufactured by Nissan ChemicalIndustries, Ltd.; and V8802 and V8803 manufactured by JGC C&C.

Additionally, the above-described silica particles may be sphericalsilica particles and are preferably deformed silica particles. In thisspecification, the “spherical silica particle” refers to, for example, aspherical or ellipsoidal silica particle, while “deformed silicaparticle” refers to a silica particle with a randomly rough surface asobserved on potato tubers. The surface area of the above-describeddeformed silica particle is larger than that of a spherical silicaparticle, and the presence of such deformed silica particles thusincreases the contact area with, for example, the above-describedpolyfunctional (meth)acrylate and successfully improves the hardness ofthe above-described hard coat layer. A transmission electron microscope(TEM) or a scanning transmission electron microscope (STEM) can be usedfor observation of the cross-section of the functional layer todetermine whether or not the reactive silica particles are deformedsilica particles as described above.

The average particle diameter of the above-described silica particles ispreferably 8 nm or more and 100 nm or less. The silica particles havingan average particle diameter of 8 nm or more can result in effectingsufficient adhesiveness to the inorganic layer 13, and 100 nm or lesscan inhibit the resulting display from turning white in color. As theupper limit of the average particle diameter of the silica particles, 65nm or less, 40 nm or less, or 25 nm or less is preferable in this order(the smaller the value, the more preferable). In cases where the silicaparticles are spherical silica particles, the average particle diameterof the silica particles corresponds to a value measured using imageprocessing software from an image obtained using a transmission electronmicroscope (TEM) or a scanning transmission electron microscope (STEM).Additionally, in cases where the silica particles are deformed silicaparticles, the average particle diameter of the silica particlescorresponds to the average between the maximum (major axis) and minimum(minor axis) values of the distance between two points on thecircumference of each deformed silica particle exhibited in the imageobtained using a transmission electron microscope (TEM) or a scanningtransmission electron microscope (STEM).

As silica particles, a combination of two or more kinds of silicaparticles is preferably used. For example, the silica particles may be acombination of the above-described reactive silica particles andnonreactive silica particles or a combination of first silica particlesand second silica particles having a smaller particle diameter than thefirst silica particles. Using a combination of the reactive silicaparticles and the nonreactive silica particles makes it possible toinhibit curl and at the same time maintain the adhesiveness to theinorganic layer 13 and scratch resistance. Additionally, using acombination of the first silica particles and the second silicaparticles makes it possible to further enhance the hardness of the hardcoat layer and thus, further enhance scratch resistance.

<Ultraviolet Absorber>

Optical films are particularly suitably used in mobile terminals such asbendable smartphones and tablet terminals, and such mobile terminals areoften used outdoors and thus each have a problem that a polarizerlocated closer to a display element than an optical film is easilydegraded by exposure to ultraviolet light. However, in cases where ahard coat layer placed on the surface of a polarizer facing toward adisplay screen contains an ultraviolet absorber, the hard coat layer canadvantageously prevent the polarizer from being degraded by exposure toultraviolet light.

Examples of the ultraviolet absorber include triazine-based ultravioletabsorbers, benzophenone-based ultraviolet absorbers, andbenzotriazole-based ultraviolet absorbers.

Examples of the above-described triazine-based ultraviolet absorbersinclude2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine,2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine,2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine,2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine,and2-[4-[(2-hydroxy-3-(2′-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine.Examples of commercially available triazine-based ultraviolet absorbersinclude Tinuvin 460, Tinuvin 477 (both are manufactured by BASF SE), andLA-46 (manufactured by ADEKA Corporation).

Examples of the above-described benzophenone-based ultraviolet absorbersinclude 2-hydroxybenzophenone, 2,4-dihydroxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone,hydroxymethoxybenzophenone sulfonate and its trihydrate, and sodiumhydroxymethoxybenzophenone sulfonate. Examples of commercially availablebenzophenone-based ultraviolet absorbers include CHMASSORB 81/FL(manufactured by BASF SE).

Examples of the above-described benzotriazole-based ultravioletabsorbers include2-ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate,2-(2H-benzotriazol-2-yl)-6-(linear and branched dodecyl)-4-methylphenol,2-[5-chloro (2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol,2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol,2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazole,2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′-(3″, 4″, 5″,6″-tetrahydrophthalimidomethyl)-5′-methylphenyl)benzotriazole,2,2-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol),and 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole.Examples of commercially available benzotriazole-based ultravioletabsorbers include KEMISORB 71 D, KEMISORB 79 (both are manufactured byChemipro Kasei Kaisha, Ltd.), JF-80, JAST-500 (both are manufactured byJohoku Chemical Co., Ltd.), ULS-1933D (manufactured by Lion SpecialtyChemicals Co., Ltd.), and RUVA-93 (manufactured by Otsuka Chemical Co.,Ltd.).

Among those ultraviolet absorbers, triazine-based andbenzotriazole-based ultraviolet absorbers are suitably used. Preferably,the ultraviolet absorber is highly soluble in a resin component includedin the functional layer, and also bleeds less out from the functionallayer after the above-described folding test. The ultraviolet absorberhas preferably been polymerized or oligomerized. As the ultravioletabsorber, polymers or oligomers containing the benzotriazole, triazine,or benzophenone backbone are preferred, specifically includingultraviolet absorbers obtained by thermal copolymerization of a(meth)acrylate containing the benzotriazole or benzophenone backbone anda methylmethacrylate (MMA) at an arbitrary ratio. In cases where theoptical film is applied to an organic light emitting diode (OLED)display device, the ultraviolet absorber can play a role in protectionof the OLED from ultraviolet light.

The ultraviolet absorber content is not limited to a particular amountbut is preferably 1 part by mass or more and 6 parts by mass or lessrelative to 100 parts by mass of solids in the functional layercomposition. In cases where the content is less than 1 part by mass, thefunctional layer may be allowed to contain only an insufficient amountof the above-described ultraviolet absorber; in cases where the contentis more than 6 parts by mass, a marked coloration and a reduction ofstrength may occur on the functional layer. The minimum content of theabove-described ultraviolet absorber is more preferably 2 parts by massor more, while the maximum content of the above-described ultravioletabsorber is more preferably 5 parts by mass or less.

<Spectral Transmittance Modifier>

The spectral transmittance modifier is an agent for modifying thespectral transmittance of an optical film. In cases where the hard coatlayer 12 contains, for example, the sesamol type benzotriazole monomerrepresented by the general formula (25) below, the above-describedspectral transmittance can be suitably achieved.

In the formula, R⁷ represents a hydrogen atom or methyl group; R⁸represents a linear or branched alkylene or oxyalkylene group having 1to 6 carbon atoms.

The above-described sesamol type benzotriazole monomer is not limited toa particular sesamol type benzotriazole monomer. Specific examples ofthe substance can include2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]ethylmethacrylate,2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]ethylacrylate,3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]propylmethacrylate,3-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]propylacrylate,4-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]butylmethacrylate,4-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl]butylacrylate,2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yloxy]ethylmethacrylate,2-[2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yloxy]ethylacrylate,2-[3-{2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl}propanoyloxy]ethylmethacrylate,2-[3-{2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl}propanoyloxy]ethylacrylate,4-[3-{2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl}propanoyloxy]butylmethacrylate,4-[3-{2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl}propanoyloxy]butylacrylate,2-[3-{2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl}propanoyloxy]ethylmethacrylate,2-[3-{2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-yl}propanoyloxy]ethylacrylate,2-(methacryloyloxy)ethyl2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate,2-(acryloyloxy)ethyl2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate,4-(methacryloyloxy)butyl2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate, and4-(acryloyloxy)butyl2-(6-hydroxybenzo[1,3]dioxol-5-yl)-2H-benzotriazole-5-carboxylate.Additionally, these sesamol type benzotriazole monomers may be usedindividually or in combination of two or more.

In cases were the above-described sesamol type benzotriazole monomer iscontained in the hard coat layer 12, the above-described sesamol typebenzotriazole monomer is preferably contained in the hard coat layer 12,for example, at a content of 15 to 30% by mass. The presence of thesesamol type benzotriazole monomer in such a content range allows theresin layer to achieve the above-described spectral transmittance. Inthe hard coat layer 12, the above-described sesamol type benzotriazolemonomer may react with a resin component included in the hard coat layer12 to be contained as an integrated part of the resulting compound, ormay be contained individually without reacting with a resin componentincluded in the hard coat layer 12.

<<Inorganic Layer>>

The inorganic layer 13 is a layer composed mainly of an inorganicsubstance, and, for example, a layer containing 55% by mass or more ofinorganic substance falls under an inorganic layer. The inorganic layer13 may contain an organic component, but is preferably composed only ofan inorganic substance. Whether a layer in contact with the hard coatlayer 12 falls under an inorganic layer can be checked by X-rayphotoelectron spectroscopy (X-Ray Photoelectron Spectroscopy: XPS orElectron Spectroscopy for Chemical Analysis: ESCA).

Examples of constituent materials for the inorganic layer 13 include:metals such as Ti, Al, Mg, and Zr; inorganic oxides such as siliconoxide (SiO_(x) (x=1 to 2)), aluminum oxide, silicon oxynitride, aluminumoxynitride, magnesium oxide, zinc oxide, indium oxide, tin oxide, andyttrium oxide; inorganic nitrides; diamondlike carbon; and the like.Among these, silicon oxide is preferable in terms of enhancingtransmittance and enhancing scratch resistance.

The inorganic layer 13 preferably contains silicon. The inorganic layer13 containing silicon makes it possible to seek a lower refractiveindex. Whether the inorganic layer contains silicon can be checked byX-ray photoelectron spectroscopy (X-Ray Photoelectron Spectroscopy: XPSor Electron Spectroscopy for Chemical Analysis: ESCA).

The inorganic layer 13 preferably has a film thickness of 10 nm or moreand 300 nm or less. The inorganic layer 13 having a film thickness of 10nm or more imparts excellent scratch resistance, and 300 nm or lessallows the adhesiveness to another layer to be favorable withoutaffecting the bendability and optical properties. As the lower limit ofthe film thickness of the inorganic layer 13, 30 nm or more, 50 nm ormore, or 80 nm or more is preferable in this order (the larger thevalue, the more preferable), and as the upper limit, 250 nm or less, 200nm or less, or 150 nm or less is preferable in this order (the smallerthe value, the more preferable). The film thickness of the inorganiclayer 13 should be determined in the same manner as the film thicknessof the hard coat layer 12.

The inorganic layer 13 preferably has a water vapor transmission rate(WVTR: Water Vapor Transmission Rate) of 100 g/(m²·24 h) or less at 40°and a relative humidity of 90%. The folding resistance is more degradedas the temperature is higher and as the relative humidity is higher.This is considered to be because water penetrates the inorganic layer13, and because the penetrating water causes the hard coat layer to behydrolyzed. Allowing the water vapor transmission rate of the inorganiclayer 13 to be 100 g/(m²·24 h) or less can decrease the amount of waterpenetrating the inorganic layer 13, and thus, can inhibit the hard coatlayer from being hydrolyzed. The water vapor transmission rate is avalue obtained by a technique in accordance with JIS K7129: 2008. Thewater vapor transmission rate can be measured using a water vaportransmission rate measurement device (product name “PERMATRAN-W3/31”;manufactured by MOCON). The arithmetic mean of three measurements isdetermined as the water vapor transmission rate.

The inorganic layer 13 can be formed, for example, by a vapor depositionmethod such as PVD or CVD. Examples of PVD methods include vacuum vapordeposition, sputtering, ion plating, and the like. Examples of vacuumvapor deposition methods include vacuum vapor deposition based on anelectron beam (EB) heating method, vacuum vapor deposition based ahigh-frequency dielectric heating method, and the like.

<<Functional Layer>>

The functional layer 14 is a layer which carries out a function in theoptical film 10, and examples of the functional layer 14 include anoptical adjustment layer, an antistatic layer, and the like. In thisregard, the functional layer 14 may carry out two or more functions. Forexample, the functional layer 14 may be a layer which carries out bothof an optical adjustment function and an antistatic function.

The functional layer 14 preferably has a film thickness of 30 nm or moreand 200 nm or less. The functional layer 14 having a film thickness of30 nm or more makes it possible to achieve sufficient adhesivenessbetween the hard coat layer 12 and the optical adjustment layer 14, and200 nm or less makes it possible to inhibit interference fringes better.As the lower limit for the functional layer 14, 50 nm or more, 70 nm ormore, or 90 nm or more is preferable in this order (the larger thevalue, the more preferable), and as the upper limit, 150 nm or less, 140nm or less, or 130 nm or less is preferable in this order (the smallerthe value, the more preferable). The film thickness of the functionallayer 14 should be determined in the same manner as the film thicknessof the hard coat layer 12.

<Optical Adjustment Layer>

In general, a resin included in a bendable light-transmitting basematerial has a high refractive index, and the light-transmitting basematerial and the hard coat layer accordingly have a large difference inrefractive index therebetween. Because of this, the difference inrefractive index between the light-transmitting base material and thehard coat layer will undesirably cause interference fringe whichexhibits iridescent nonuniformity. An optical adjustment layer is alayer for inhibiting the generation of interference fringe. Therefractive index of the optical adjustment layer is preferably lowerthan that of the light-transmitting base material 11 and higher thanthat of the hard coat layer 12, in terms of inhibiting the generation ofinterference fringe. The refractive index of the optical adjustmentlayer can be measured, for example, by the Becke method. In measuringthe refractive index of the optical adjustment layer in accordance withthe Becke method, 10 fragments are cut out from an optical adjustmentlayer, the 10 cut fragments are each measured for refractive index usinga refractive index standard liquid in accordance with the Becke method,and the average value of the 10 refractive index measurements of thefragments is regarded as the refractive index of the optical adjustmentlayer. The refractive index of the light-transmitting base material 11and that of the hard coat layer 12 can be measured in the same manner asthat of the optical adjustment layer.

The refractive index difference between the optical adjustment layer andthe hard coat layer 12 (the refractive index of the optical adjustmentlayer−the refractive index of the hard coat layer) is preferably 0.005or more and 0.100 or less. This refractive index difference of 0.005 ormore causes interfacial reflection between the optical adjustment layerand the hard coat layer 12, but the interfacial reflection can becontrolled at a level which causes no visible interference fringe, and0.100 or less causes slight visible interference fringe, but theinterference fringe can be controlled at a level which is notproblematic for practical usage. The lower limit of the refractive indexdifference is more preferably 0.007 or more, while the upper limit ismore preferably 0.090 or less. The refractive index of the opticaladjustment layer may be 0.010 or more and 0.080 or less.

The optical adjustment layer may be composed only of a resin, butpreferably contains a binder resin and particles for adjustment of therefractive index. Additionally, the optical adjustment layer may furthercontain an antistatic agent to exert an antistatic function besides theoptical adjustment function. The binder resin for the optical adjustmentlayer is preferably at least one resin selected from the groupconsisting of (meth)acrylic resins, cellulose resins, urethane resins,vinyl chloride resins, polyester resins, polyolefin resins,polycarbonate, nylon, polystyrene, and ABS resins. The particles for theoptical adjustment layer 14 are preferably at least one selected fromthe group consisting of: low refractive index particles such as ofsilica or magnesium fluoride; metal oxide particles such as of titaniumoxide or zirconium oxide; inorganic pigments such as cobalt blue; andthe like. Among these, a combination of a polyester resin and metaloxide particles such as of titanium oxide or zirconium oxide is morepreferable in terms of adjusting adhesiveness and refractive indexdifference.

<Antistatic Layer>

The antistatic layer contains an antistatic agent. Examples ofantistatic agents include an ionic conductive antistatic agent and anelectronic conductive antistatic agent, and an ionic conductiveantistatic agent is preferable in terms of compatibility with binderresins.

Examples of the ionic conductive antistatic agent include: cationicantistatic agents such as quaternary ammonium salts and pyridium salts;anionic antistatic agents such as alkali metal salts (for example,lithium salts, sodium salts, potassium salts, and the like) such as ofsulfonic acid, phosphoric acid, and carboxylic acid; amphotericantistatic agents such as amino acid-based and amino acid sulfate-basedones; nonionic antistatic agents such as aminoalcohol-based,glycerin-based, and polyethylene glycol-based ones; and the like. Amongthese, quaternary ammonium salts and lithium salts are preferable interms of exhibiting excellent compatibility with binder resins.

Examples of the electronic conductive antistatic agent include:electroconductive polymers such as polyacetylene-based andpolythiophene-based ones; electroconductive particles such as metalparticles and metal oxide particles. Among these, preferable ones are:antistatic agents obtained by combining a dopant with anelectroconductive polymer such as polyacetylene or polythiophene; metalparticles; and metal oxide particles. The electroconductive polymer isalso allowed to contain electroconductive particles.

Specific examples of the antistatic agent composed of anelectroconductive polymer include electroconductive polyers such aspolyacetylene, polyaniline, polythiophene, polypyrrole, polyphenylenesulfide, poly(1,6-heptadiyne), polybiphenylene (polyparaphenylene),polyparaphinylene sulfide, polyphenyl acetylene, poly(2,5-thienylene),and derivatives thereof. Preferable examples include polythiophene-basedelectroconductive organic polymers (for example,3,4-ethylenedioxythiophene (PEDOT)).

Use of the antistatic agent composed of an electroconductive organicpolymer affords low humidity dependence to maintain an antistaticproperty for a long period of time; additionally, makes it possible toachieve high transparency and a low haze value; and furthermore, affordssignificantly enhanced hard coat properties, particularly high pencilhardness, scratch resistance to steel wool, and the like.

Examples of metals included in the metal particles include, but are notparticularly limited to: Au, Ag, Cu, Al, Fe, Ni, Pd, Pt, and the likeused singly; and alloys of these metals. Additionally, examples of metaloxides included in the metal oxide particles include, but are notparticularly limited to, tin oxide (SnO₂), antimony oxide (Sb₂O₅),antimony-doped tin oxide (ATO), tin-doped indium oxide (ITO),aluminum-doped zinc oxide (AZO), fluorine-doped tin oxide (FTO), zincoxide (ZnO), and the like.

The antistatic agent content is not limited to a particular value, butis preferably 1 part by mass or more and 50 parts by mass or lessrelative to 100 parts by mass of polymerizable compound in theantistatic layer composition. The amount of 1 part by mass or moreallows the above-described antistatic property to be sufficient, and 50parts by mass or less makes it possible to obtain a highly transparentfilm having a small haze value and favorable total light transmittance.The lower limit of the antistatic agent content is more preferably 10parts by mass or more, while the upper limit is more preferably 40 partsby mass or less.

<<Optical Film Production Method>>

The optical film 10 can be produced, for example, as follows. First, afunctional layer composition for forming a functional layer 14 isapplied on one surface of the light-transmitting base material 11 with acoating apparatus such as a bar coater to form a coating film of thefunctional layer composition. Here, the functional layer composition isan optical adjustment layer composition, but may also be an antistaticlayer composition.

<Functional Layer Composition>

The functional layer composition contains a binder resin precursor,particles of metal oxide or the like, and a solvent. If necessary, thefunctional layer composition may contain at least one of: low refractiveindex particles such as of silica or magnesium fluoride; inorganicpigments such as cobalt blue; leveling agents; and polymerizationinitiators. In cases where a polyester resin is used as the binder resinprecursor, the functional layer composition may additionally contain, ifnecessary, one or more resins selected from the group consisting of(meth)acrylic resins, cellulose resins, urethane resins, vinyl chlorideresins, polyolefin resins, polycarbonate, nylon, polystyrene, and ABSresins.

After the coating film of the functional layer composition is formed,the coating film is heated and dried, for example, at a temperature of40° C. or higher and 200° C. or lower for a period of 10 seconds to 120seconds by various known techniques to evaporate the solvent or cure thecoating film. If necessary, the coating film is also exposed to ionizingradiation such as ultraviolet light to form a functional layer 14.

After the functional layer 14 is formed, a hard coat layer compositionfor forming a hard coat layer 12 is applied on the functional layer 14with a coating apparatus such as a bar coater to form a coating film ofthe hard coat layer composition.

<Hard Coat Layer Composition>

The hard coat layer composition contains: a polymerizable compound whichis cured to become a binder resin 12A; and inorganic particles 12B. Thehard coat layer composition may additionally contain an ultravioletabsorber, a spectral transmittance modifier, a leveling agent, asolvent, and a polymerization initiator, as necessary.

(Solvent)

Examples of the above-described solvent include alcohols (for example,methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol,t-butanol, benzyl alcohol, PGME, ethylene glycol, diacetone alcohol),ketones (for example, acetone, methyl ethyl ketone, methyl isobutylketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone,diethyl ketone, diacetone alcohol), esters (methyl acetate, ethylacetate, butyl acetate, n-propyl acetate, isopropyl acetate, methylformate, PGMEA), aliphatic hydrocarbons (for example, hexane,cyclohexane), halogenated hydrocarbons (for example, methylene chloride,chloroform, carbon tetrachloride), aromatic hydrocarbons (for example,benzene, toluene, xylene), amides (for example, dimethylformamide,dimethylacetamide, n-methylpyrrolidone), ethers (for example, diethylether, dioxane, tetrahydrofurane), ether alcohols (for example,1-methoxy-2-propanol), and carbonates (dimethyl carbonate, diethylcarbonate, ethylmethyl carbonate). These solvents may be usedindividually or in combination of two or more. Among those solvents,methyl isobutyl ketone and methyl ethyl ketone are preferred as theabove-described solvent in terms of the ability to dissolve or dispersecomponents such as urethane (meth)acrylate and other additives andthereby to apply the above-described resin layer composition in asuitable manner.

(Polymerization Initiator)

The polymerization initiator is a component which degrades, when exposedto ionizing radiation or heat, and generates radicals to initiate orpromote polymerization (cross-linking) of a polymerizable compound.

The polymerization initiator is not limited to a particularpolymerization initiator as long as it can generate a substance thatinitiates a radical polymerization by exposure to ionizing radiation orheat. Any known polymerization initiator can be used without anyparticular limitation, and specific examples include acetophenones,benzophenones, Michler's benzoyl benzoate, α-amyloxime esters,thioxantones, propyophenones, benzyls, benzoins, and acylphosphineoxides. Additionally, a photosensitizer is preferably mixed for use, andspecific examples of the photosensitizer include n-butylamine,triethylamine, and poly-n-butylphosphine.

After the coating film of the hard coat layer composition is formed, thecoating film is heated and dried at a temperature of, for example, 30°C. or higher and 120° C. or lower for a period of 10 seconds to 120seconds by various known techniques to evaporate the solvent.

The coating film is dried and then cured by exposure to ionizingradiation such as ultraviolet light to form a hard coat layer 12.

After the hard coat layer 12 is formed, an inorganic layer 13 is formedso as to be in contact with the hard coat layer 12 using a vapordeposition method such as sputtering. Consequently, the optical film 10shown in FIG. 1 is obtained.

<<<Image Display Device>>>

The optical film 10 may be incorporated into a foldable image displaydevice and then used. FIG. 4 depicts the schematic diagram of the imagedisplay device according to the present embodiment. As shown in FIG. 4,a housing 41 for housing a battery and the like, a protective film 42, adisplay panel 43, a touch sensor 44, a circularly polarizing plate 45,and the optical film 10 are mainly laminated in this order toward theobserver in the image display device 40. A light-transmitting adhesive46 such as, for example, OCA (optical clear adhesive) is placed alongthe interfaces between the display panel 43 and the touch sensor 44,between the touch sensor 44 and the circularly polarizing plate 45, andbetween the circularly polarizing plate 45 and the optical film 10, andthese members are fixed to each other with the light-transmittingadhesive 46.

In the optical film 10, the hard coat layer 12 is located on theobserver's side of the light-transmitting base material 11. For theimage display device 40, the surface 11A of the optical film 10 isconfigured to be the surface 40A of the image display device 40.

In the image display device 40, the display panel 43 is an organic lightemitting diode panel containing an organic light emitting diode and thelike. The touch sensor 44 is located closer to the display panel 43 thanthe circularly polarizing plate 45 but may be placed between thecircularly polarizing plate 45 and the optical film 10. Additionally,the touch sensor 44 may be an on-cell type or an in-cell type.

The present inventors have vigorously made studies on the scratchresistance of an optical film in which an inorganic layer is formed on ahard coat layer, and have discovered that the scratch resistance can beenhanced by allowing the hard coat layer to contain inorganic particles,allowing the hard coat layer to have a film thickness of 1 μm or more,and allowing the hard coat layer to have an indentation hardness of 200MPa or more. This is considered to be because blending a suitable hardcoat layer with suitable inorganic particles has made it possible toensure firm adhesiveness to an inorganic layer and enabled the hard coatlayer to achieve higher hardness. The present embodiment allows the hardcoat layer 12 containing the binder resin 12A and the inorganicparticles 12B to have a film thickness of 1 μm or more and allows thehard coat layer 12 to have an indentation hardness of 200 MPa or more,and thus, can provide the optical film 10 having excellent scratchresistance.

When the surface of the hard coat layer is subjected to a steel wooltest, the inorganic particles tend to fall off. Because of this, it isconsidered to be preferable, in terms of enhancing scratch resistance,that the hard coat layer does not contain inorganic particles, but inthe present embodiment, the inorganic layer 13 is formed on the hardcoat layer 12, thus making it possible to inhibit the inorganicparticles 12B in the hard coat layer 12 from falling off in a steel wooltest. Thus, containing the inorganic particles 12 makes it possible toenhance the hardness of the hard coat layer 12 and enhance the scratchresistance.

Second Embodiment

An optical film, a laminate, a polarizing plate and an image displaydevice according to the second embodiment of the present invention arenow described with reference to the drawings. FIG. 5 depicts theschematic diagram of the polarizing plate in which the optical filmaccording to the present embodiment is incorporated. In FIG. 5, theelements indicated by the same reference numbers as in FIG. 1 are thesame as those indicated in FIG. 1, and further description is thusomitted.

<<<Optical Film>>>

The optical film 50 shown in FIG. 5 includes a light-transmitting basematerial 11, a hard coat layer 51, and an inorganic layer 13 in thisorder in the same manner as the optical film 10. In FIG. 5, the surface50A of the optical film 50 corresponds to the surface 13A of theinorganic layer 13, and the back surface 50B corresponds to the oppositesurface of the light-transmitting base material 11 from the hard coatlayer 51 side. The physical properties of the optical film 50 are thesame as those of the optical film 10, and the description thereof isthus omitted here.

<<Hard Coat Layer>>

The hard coat layer 51 has an indentation hardness of 200 MPa or morefor the same reason as described in the section on the hard coat layer12, and also has a film thickness of 1 μm or more. The preferable upperlimit and lower limit of the indentation hardness and film thickness ofthe hard coat layer 51 are the same as the preferable upper limit andlower limit of the indentation hardness and film thickness of the hardcoat layer 12. The physical properties and the like of the hard coatlayer 51 are the same as those of the hard coat layer 12, and thedescription thereof is thus omitted here.

The hard coat layer 51 contains at least one of a metallic element and ametalloid element. The hard coat layer 51 containing at least one of ametallic element and a metalloid element makes it possible to enhancethe adhesiveness to the inorganic layer 13 and thus enhance scratchresistance. The metallic element may be any of typical metallic elementssuch as aluminum and tin and transition metallic elements such aszirconium and titanium. Additionally, examples of metalloid elementsinclude boron, silicon, germanium, arsenic, antimony, tellurium, and thelike. Whether the hard coat layer contains any of the elements can bechecked by the following method. First, a piece having a size of 1 mm×6mm was cut out from an optical film, and the piece was cut at an angleof 2° or less with the plane using a microtome (product name“Ultramicrotome EM UC7”; manufactured by Leica Microsystems GmbH) so asto have a film thickness equal to or greater than the film thickness ofthe inorganic layer and to expose the hard coat layer. Then, an X-rayphotoelectron spectroscope (ESCA, product name “KRATOS Nova”;manufactured by Shimadzu Corporation) is used to carry out elementalanalysis on the surface obtained by cutting as above-described. Thismakes it possible to check whether the hard coat layer contains at leastone of a metallic element and a metalloid element.

The atomic ratio of the total of the metallic element and the metalloidelement contained in the hard coat layer 51 is preferably 1.5% or moreand 30% or less as measured by X-ray photoelectron spectroscopy.Allowing the atomic ratio of the total of the metallic element and themetalloid element to be 1.5% or more makes it possible to enhance theadhesiveness to the inorganic layer 13, and additionally, 30% or lessmakes it possible to maintain the bendability. The atomic ratio of thetotal of the metallic element and the metalloid element should bemeasured using an X-ray photoelectron spectroscope (ESCA, product name“KRATOS Nova”; manufactured by Shimadzu Corporation) on the surfaceobtained by cutting for the purpose of carrying out the elementalanalysis. The lower limit of the atomic ratio of the total amount of themetallic element and the metalloid element in the hard coat layer 51 is2% or more, more preferably 5% or more, (the larger the value, the morepreferable), and the upper limit is 25% or less, more preferably 20% orless, (the smaller the value, the more preferable).

The hard coat layer 51 preferably contains a silicone resin 51A andinorganic particles 51B in terms of further enhancing scratchresistance. However, the hard coat layer 51 does not have to containboth the silicone resin 51A and the inorganic particles 51B if the hardcoat layer 51 contains at least one of a metallic element and ametalloid element. For example, in cases where the hard coat layercontains a silicone resin, the hard coat layer contains silicon derivedfrom the silicone resin, and accordingly, does not have to contain theinorganic particles 51B. In cases where the hard coat layer containssilica particles as inorganic particles, the hard coat layer containssilicon derived from the silica particles, and accordingly, does nothave to contain a silicone resin. As used herein, a “silicone resin”means a polymer compound having a main backbone formed with a siloxanebond (a bond between silicon and oxygen). The hard coat layer 51 maycontain an additive such as an ultraviolet absorber or a spectraltransmittance modifier in addition to the silicone resin 51A andinorganic particles 51B.

<Silicone Resin>

The silicone resin 51A is preferably a polymer (cured product) of apolymerizable compound containing silsesquioxane represented by thegeneral formula (R⁹SiO_(1.5))_(n) having a polymerizable functionalgroup. In the formula, R⁹ is a polymerizable functional group such as aradical polymerizable functional group or a cationic polymerizablefunctional group, and n is an integer of 1 or greater. The polymerizablecompound may contain another polymerizable compound in addition to thesilsesquioxane, and may also be the silsesquioxane alone. The siliconeresin 51A contains such a polymer of a polymerizable compound containingsilsesquioxane, resulting in making it possible to have firmadhesiveness to the inorganic layer. Examples of radical polymerizablefunctional groups include ethylenic unsaturated groups such as a(meth)acryloyl group, vinyl group, and allyl group, and examples ofcationic polymerizable functional groups include an epoxy group and anoxetanyl group. Containing such a radical polymerizable functional groupand a cationic polymerizable functional group enables thesilsesquioxanes to link therebetween, making it possible to obtain apolymer.

Examples of structures of silsesquioxane include, but are notparticularly limited to: cage structures such as a complete cagestructure and an incomplete cage structure; a ladder structure; a randomstructure; and the like, and may be any of these structures. Examples ofcommercially available silsesquioxane include Glycidylpolysilsesquioxane cage mixture manufactured by Construe Chemical Co.,Ltd. and photo-curable SQ series manufactured by Toagosei Co., Ltd.

The polymerizable compound for forming the silicone resin 51A maycontain, instead of the silsesquioxane, the following:dimethylpolysiloxane having a radical polymerizable functional groupsuch as a (meth)acryloyl group; a silicone oligomer having analkoxysilyl group; and/or a silicone polymer. The silicone oligomer andsilicone polymer preferably have a polymerizable functional group suchas a radical polymerizable functional group or a cationic polymerizablefunctional group in terms of enabling the hardness of the hard coatlayer to be further enhanced.

Examples of commercially available dimethylpolysiloxane having a radicalpolymerizable functional group include the KR series manufactured byShin-Etsu Chemical Co., Ltd., for example, KP-410, KP-411, KP-412,KP-413, KP-414, KP-415, KP-423 (which are all of a dual-end type),KP-416, KP418, KP-422 (which are all of a single-end type), and KP-420(which is of a side chain type).

Examples of commercially available silicone oligomers having analkoxysilyl group include: KR-500, KR-515, KC-895, and X-40-9225manufactured by Shin-Etsu Chemical Co., Ltd.; and the like.Additionally, examples of ultrahigh molecular weight silicone resinsinclude: KR-251 manufactured by Shin-Etsu Chemical Co., Ltd.; and thelike.

<Inorganic Particles>

The inorganic particles 51B are the same as the inorganic particles 12Bdescribed in the first embodiment, and the description is thus omittedhere.

The present inventors have vigorously made studies on the scratchresistance of an optical film in which an inorganic layer is formed on ahard coat layer, and have discovered that the scratch resistance can beenhanced by allowing the hard coat layer to contain at least one of ametallic element and a metalloid element, allowing the hard coat layerto have a film thickness of 1 μm or more, and allowing the hard coatlayer to have an indentation hardness of 200 MPa or more. This isconsidered to be because allowing the hard coat layer to contain atleast one of a metallic element and a metalloid element has made itpossible to ensure firm adhesiveness to an inorganic layer and enabledthe hard coat layer to achieve higher hardness. The present embodimentallows the hard coat layer 51 containing at least one of a metallicelement and a metalloid element to have a film thickness of 1 μm or moreand allows the hard coat layer 51 to have an indentation hardness of 200MPa or more, and thus, can provide the optical film 50 having excellentscratch resistance.

When the surface of the hard coat layer is subjected to a steel wooltest, the inorganic particles tend to fall off. Because of this, it isconsidered to be preferable, in terms of enhancing scratch resistance,that the hard coat layer does not contain inorganic particles, but inthe present embodiment, the inorganic layer 13 is formed on the hardcoat layer 51, thus making it possible to inhibit the inorganicparticles 51B in the hard coat layer 51 from falling off in a steel wooltest. Thus, containing the inorganic particles 51B makes it possible toenhance the hardness of the hard coat layer 51 and enhance the scratchresistance.

<<<Image Display Device>>>

The optical film 50 may be incorporated into a foldable image displaydevice and then used. FIG. 6 depicts the schematic diagram of the imagedisplay device according to the present embodiment. The image displaydevice 60 shown in FIG. 6 includes an optical film 50. The image displaydevice 60 is the same as the image display device 40 except that theoptical film 10 is replaced with the optical film 50, and thedescription thereof is thus omitted here.

EXAMPLES

Now, the present invention will be described in more detail by way ofExamples. However, the present invention is not limited to thoseExamples. The phrase “a converted value based on 100% solids” belowmeans a value determined based on the assumption that the content ofsolids diluted in a solvent is 100%.

<Preparation of Hard Coat Layer Compositions>

First, the following components were combined to meet the compositionrequirements indicated below and thereby obtain hard coat layercompositions.

(Hard Coat Layer Composition 1)

-   -   Polyester acrylate (product name “M-9050”; manufactured by        Toagosei Co., Ltd.): 50 parts by mass    -   Silica particles (product name “MIBK-SD”; manufactured by Nissan        Chemical Industries, Ltd.): 50 parts by mass    -   Polymerization initiator (1-hydroxycyclohexyl phenyl ketone;        product name “Irgacure®184”; manufactured by BASF Japan Ltd.): 5        parts by mass    -   Methyl isobutyl ketone: 100 parts by mass

(Hard Coat Layer Composition 2)

-   -   Polyester acrylate (product name “M-9050”; manufactured by        Toagosei Co., Ltd.): 67 parts by mass    -   Silica particles (product name “MIBK-SD”; manufactured by Nissan        Chemical Industries, Ltd.): 33 parts by mass    -   Polymerization initiator (1-hydroxycyclohexyl phenyl ketone;        product name “Irgacure®184”; manufactured by BASF Japan Ltd.): 5        parts by mass    -   Methyl isobutyl ketone: 100 parts by mass

(Hard Coat Layer Composition 3)

-   -   Polyester acrylate (product name “M-9050”; manufactured by        Toagosei Co., Ltd.): 90 parts by mass    -   Silica particles (product name “MIBK-SD”; manufactured by Nissan        Chemical Industries, Ltd.): 10 parts by mass    -   Polymerization initiator (1-hydroxycyclohexyl phenyl ketone;        product name “Irgacure®184”; manufactured by BASF Japan Ltd.): 5        parts by mass    -   Methyl isobutyl ketone: 100 parts by mass

(Hard Coat Layer Composition 4)

-   -   Alkoxylated dipentaerythritol acrylate (product name        “A-DPH-12E”; manufactured by Shin-Nakamura Chemical Co., Ltd.):        50 parts by mass    -   Silica particles (product name “MIBK-SD”; manufactured by Nissan        Chemical Industries, Ltd.): 50 parts by mass    -   Polymerization initiator (1-hydroxycyclohexyl phenyl ketone;        product name “Irgacure®184”; manufactured by BASF Japan Ltd.): 5        parts by mass    -   Methyl isobutyl ketone: 100 parts by mass

(Hard Coat Layer Composition 5)

-   -   Glycidyl polysilsesquioxane (product name “Glycidyl        polysilsesquioxane cage mixture”; manufactured by Construe        Chemical Co., Ltd.): 100 parts by mass    -   Polymerization initiator (tri-p-tolylsulfonium        hexafluorophosphate; manufactured by Tokyo Chemical Industry        Co., Ltd.): 5 parts by mass    -   1-methoxy-2-propanol: 100 parts by mass

(Hard Coat Layer Composition 6)

-   -   Polyester acrylate (product name “M-9050”; manufactured by        Toagosei Co., Ltd.): 100 parts by mass    -   Polymerization initiator (1-hydroxycyclohexyl phenyl ketone;        product name “Irgacure®184”; manufactured by BASF Japan Ltd.): 5        parts by mass    -   Methyl isobutyl ketone: 100 parts by mass

(Hard Coat Layer Composition 7)

-   -   Polypropylene glycol diacrylate (product name “M-220”;        manufactured by Toagosei Co., Ltd.): 90 parts by mass    -   Silica particles (product name “MIBK-SD”; manufactured by Nissan        Chemical Industries, Ltd.): 10 parts by mass    -   Polymerization initiator (1-hydroxycyclohexyl phenyl ketone;        product name “Irgacure®184”; manufactured by BASF Japan Ltd.): 5        parts by mass    -   Methyl isobutyl ketone: 100 parts by mass

<Preparation of Optical Adjustment Layer Compositions>

The following components were combined to meet the compositionrequirements indicated below and thereby obtain optical adjustment layercompositions.

(Optical Adjustment Layer Composition 1)

-   -   Urethane-modified polyester resin (product name “UR-3200”;        manufactured by Toyobo Co., Ltd.): 85 parts by mass (a converted        value based on 100% solids)    -   Zirconium oxide (with an average particle diameter of 20 nm;        manufactured by CIK NanoTek Corporation): 15 parts by mass (a        converted value based on 100% solids)    -   Methyl isobutyl ketone (MIBK): 170 parts by mass

<Production of Polyimide Base Material>

In a 500 ml separable flask, 278.0 g of dehydrated dimethylacetamide and8.1 g (33 mmol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (AprTMOS)were dissolved to make a solution, which was controlled at a liquidtemperature of 30° C., and to the solution, 18.1 g (41 mmol) of4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was graduallyadded with the temperature rise regulated to 2° C. or less. Theresulting mixture was stirred using a mechanical stirrer for one hour.To the resulting solution, 46.1 g (131 mmol) of2,2′-bis(trifluoromethyl)benzidine (TFMB) was added, followed byverifying that they were completely dissolved, and then 51.8 g (122mmol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) wasgradually added in several installments with the temperature riseregulated to 2° C. or less, to synthesize a polyimide precursor solution(1) (having a solid content of 30 wt %) in which a polyimide precursor 1was dissolved.

The polyimide precursor solution (1) was cooled to room temperature, andto the solution, 196.8 g of dehydrated dimethylacetamide was added. Theresulting mixture was stirred so as to be uniform. To the resultingmixture, 128.9 g of (1.63 mol) of pyridine, which was a catalyst, and167.7 g (1.63 mol) of acetic anhydride were added, and then, theresulting mixture was stirred at room temperature for 24 hours tosynthesize a polyimide solution. Into a 5 L separable flask, 400.0 g ofthe resulting polyimide solution was transferred, 119.2 g of butylacetate was added to the solution, and the resulting mixture was stirredso as to be uniform. Next, 688.0 g of methanol was gradually added tothe resulting mixture to obtain a solution which was slightly turbid. Tothe turbid solution, 2.064 kg of methanol was added all at once toobtain white slurry. The slurry was filtrated and washed with methanolfive times to obtain 65.0 g of polyimide resin (1).

To 42.2 g of butyl acetate, 10.0 g of the polyimide resin (1) was added,and the resulting mixture was stirred at room temperature for one hourto obtain a polyimide solution. The polyimide solution was degassedusing a tabletop ultrasonic cleaning device (product name “UT-104”;manufactured by Sharp Corporation) for ten minutes, taken out, and leftto stand at room temperature for one hour. The polyimide solution whichhad been left to stand was applied onto a polyethylene terephthalate(PET) film (product name “LUMIRROR T60”; manufactured by TorayIndustries, Inc.) having a thickness of 250 μm, dried in a circulationoven at 40° C. for ten minutes and at 150° C. for ten minutes, thenremoved from the PET film, and further dried at 150° C. for one hour toobtain a polyimide base material having a size of A5 (148 mm×210 mm) anda thickness of 50 μm. Here, the thickness of the polyimide base materialis defined as the arithmetic mean of film thickness values measured at10 different locations, where a cross-section of the polyimide basematerial is photographed using a scanning electron microscope (SEM) andthe thickness of the polyimide base material is measured at the 10locations within the image of the cross-section.

Example 1

A polyimide base material having a refractive index of 1.630 and athickness of 50 μm (product name “Neopulim”; manufactured by MitsubishiGas Chemical Company, Inc.) was prepared as a light-transmitting basematerial, and the hard coat layer composition 1 was applied on a firstsurface of the polyimide base material with a bar coater to form acoating film. Then, the formed coating film was heated at 70° C. for oneminute to evaporate the solvent in the coating film, and was thenexposed to ultraviolet light to a cumulative light dose of 200 mJ/cm² ina nitrogen atmosphere with an ultraviolet irradiation device (with an Hbulb as a light source; manufactured by Fusion UV Systems Inc.) to becured and form a hard coat layer having a refractive index of 1.521 anda film thickness of 4 μm. Lastly, an inorganic layer having a filmthickness of 100 nm and composed of SiO_(x) (x=1 to less than 2) wasformed on the surface of the hard coat layer by sputtering to obtain anoptical film.

The thickness of the polyimide base material is defined as thearithmetic mean of thickness values measured at 10 different locations,where a cross-section of the polyimide base material is photographedusing a scanning electron microscope (SEM) and the thickness of thepolyimide base material is measured at the 10 locations within the imageof the cross-section. The film thickness of the hard coat layer wasdefined as the arithmetic mean of film thickness values measured at 10different locations, where a cross-section of the hard coat layer wasphotographed using a scanning transmission electron microscope (STEM)(product name “S-4800”; manufactured by Hitachi High-TechnologiesCorporation) and the film thickness of the hard coat layer was measuredat the 10 locations within the image of the cross-section. Thecross-section of the hard coat layer was photographed in thebelow-mentioned manner. First of all, a piece of 1 mm×10 mm cut out fromthe optical film was embedded in an embedding resin to prepare a block,and homogeneous sections having a thickness of 70 nm or more and 100 nmor less and having no openings or the like were cut out from the blockaccording to a commonly used sectioning technique. For the preparationof sections, an “Ultramicrotome EM UC7” (Leica Microsystems GmbH) or thelike was used. Then, these homogeneous sections having no openings orthe like were used as measurement samples. Subsequently, cross-sectionalimages of the measurement sample were acquired using a scanningtransmission electron microscope (STEM). The cross-sectional images wereacquired by setting the detector to “TE,” the accelerating voltage to“30 kV,” and the emission current to “10 μA” in the STEM observation.The focus, contrast, and brightness were appropriately adjusted at amagnification of 5000 to 200,000 times, so that each layer could beidentified by observation. Furthermore, the beam monitor aperture, theobjective lens aperture, and the WD were respectively set to “3,” “3,”and “8 mm,” in acquirement of cross-sectional images. The film thicknessof the inorganic layer was measured in the same manner as the filmthickness of the hard coat layer. The refractive indices of thepolyimide base material and the like and the hard coat layer weredetermined by the Becke method in accordance with the method B in JISK7142:2008. In determination of the refractive index of the polyimidebase material in accordance with the Becke method, 10 fragments were cutout from a polyimide base material, the 10 cut fragments were eachmeasured for refractive index using a sodium D line having a wavelengthof 589 nm and a refractive index standard liquid, and the average valueof the 10 refractive index measurements of the fragments is regarded asthe refractive index of the polyimide base material. The refractiveindex of the hard coat layer was also determined in accordance with theBecke method in the same manner as the refractive index of the polyimidebase material determined in accordance with the above-described Beckemethod. Also in Examples 2 to 7 and Comparative Examples 1 to 4, thethickness and refractive index of the polyimide base materials and thelike were measured by the same methods as in Example 1.

Example 2

In Example 2, an optical film was obtained in the same manner as inExample 1, except that the hard coat layer composition 2 was usedinstead of the hard coat layer composition 1.

Example 3

In Example 3, an optical film was obtained in the same manner as inExample 1, except that the hard coat layer composition 3 was usedinstead of the hard coat layer composition 1.

Example 4

In Example 4, an optical film was obtained in the same manner as inExample 1, except that the hard coat layer composition 4 was usedinstead of the hard coat layer composition 1.

Example 5

In Example 5, an optical film was obtained in the same manner as inExample 1, except that the film thickness of the hard coat layer was 2μm.

Example 6

In Example 6, an optical film was obtained in the same manner as inExample 1, except that the film thickness of the hard coat layer was 10μm.

Example 7

In Example 7, an optical film was obtained in the same manner as inExample 1, except that the film thickness of the hard coat layer was 20μm.

Example 8

A polyimide base material having a refractive index of 1.630 and athickness of 50 μm (product name “Neopulim”; manufactured by MitsubishiGas Chemical Company, Inc.) was prepared as a light-transmitting basematerial, and the optical adjustment layer composition 1 was applied ona first surface of the polyimide base material with a bar coater to forma coating film. Then, the formed coating film was heated at 90° C. forone minute to evaporate the solvent in the coating film to form anoptical adjustment layer having a refractive index of 1.562 and a filmthickness of 100 nm. After the formation of the optical adjustmentlayer, the hard coat layer composition 1 was applied on the surface ofthe optical adjustment layer with a bar coater to form a coating film.Then, the formed coating film was heated at 70° C. for one minute toevaporate the solvent in the coating film, and was then exposed toultraviolet light to a cumulative light dose of 200 mJ/cm² in a nitrogenatmosphere with an ultraviolet irradiation device (with an H bulb as alight source; manufactured by Fusion UV Systems Inc.) to be cured andform a hard coat layer having a refractive index of 1.521 and a filmthickness of 4 μm. Lastly, an inorganic layer having a film thickness of100 nm and composed of SiO_(x) (x=1 to less than 2) was formed on thesurface of the hard coat layer by sputtering to obtain an optical film.The film thickness of the optical adjustment layer was defined as thearithmetic mean of thickness values measured at 10 different locations,where a cross-section of the optical adjustment layer was photographedusing a scanning transmission electron microscope (STEM) (product name“S-4800”; manufactured by Hitachi High-Technologies Corporation) and thethickness of the optical adjustment layer was measured at the 10locations within the image of the cross-section. The film thickness ofthe optical adjustment layer was measured in the same manner as the filmthickness of the hard coat layer. Additionally, the refractive index ofthe optical adjustment layer was determined by the Becke method inaccordance with the method B in JIS K7142:2008 in the same manner asthat of the polyimide base material and the like.

Example 9

In Example 9, an optical film was obtained in the same manner as inExample 1, except that the polyimide base material 1 produced abovemethod was used instead of a polyimide base material (product name“Neopulim”; manufactured by Mitsubishi Gas Chemical Company, Inc.).

Example 10

In Example 10, an optical film was obtained in the same manner as inExample 1, except that the hard coat layer composition 5 was usedinstead of the hard coat layer composition 1.

Comparative Example 1

In Comparative Example 1, an optical film was obtained in the samemanner as in Example 1, except that the hard coat layer composition 6was used instead of the hard coat layer composition 1.

Comparative Example 2

In Comparative Example 2, an optical film was obtained in the samemanner as in Example 1, except that the hard coat layer composition 7was used instead of the hard coat layer composition 1.

Comparative Example 3

In Comparative Example 3, an optical film was obtained in the samemanner as in Example 1, except that the film thickness of the hard coatlayer was 0.8 μm.

<Measurement of Indentation Hardness>

The indentation hardness of the hard coat layer of the optical filmaccording to each of Examples and Comparative Examples was measured.Specifically, a piece having a size of 1 mm×10 mm was cut out from theoptical film and embedded in an embedding resin to prepare a block, andhomogeneous sections having a thickness of 70 nm or more and 100 nm orless and having no openings or the like were cut out from the blockaccording to a commonly used sectioning technique. For the preparationof sections, an “Ultramicrotome EM UC7” (Leica Microsystems GmbH) wasused. Then, the block remaining after cutting out the homogeneoussections having no openings or the like was used as a measurementsample. Subsequently, a Berkovich indenter (a trigonal pyramid, TI-0039,manufactured by BRUKER Corporation) as the above-described indenter waspressed perpendicularly into the cross-section of the hard coat layer inthe cross-section of the measurement sample obtained after cutting outthe sections, wherein the indenter was pressed up to the maximumpressing load of 500 μN over 25 seconds under the below-mentionedmeasurement conditions. Here for the optical film according to each ofExamples 1 to 7, 9, and 10 and Comparative Examples 1 to 3, a Berkovichindenter was pressed into a part of the hard coat layer in order toavoid the influence of the polyimide base material and the inorganiclayer and avoid the influence of the side edges of the hard coat layer,wherein the part is 500 nm away into the central side of the hard coatlayer from the interface between the polyimide base material and thehard coat layer, 500 nm away into the central side of the hard coatlayer from the interface between the hard coat layer and the inorganiclayer, and 500 nm away into the central side of the hard coat layer fromboth side edges of the hard coat layer. For the same reason, a Berkovichindenter was pressed into a part of the hard coat layer in the opticalfilm according to Example 8, wherein the part is 500 nm away into thecentral side of the hard coat layer from the interface between theoptical adjustment layer and the hard coat layer, 500 nm away into thecentral side of the hard coat layer from the interface between the hardcoat layer and the inorganic layer, and 500 nm away into the centralside of the hard coat layer from both side edges of the hard coat layer.Subsequently, the intender was held at the position for a certain periodof time to relax the residual stress, and then unloaded over 25 secondsto measure the maximum load after the relaxation, and the maximum loadP_(max) (μN) and the contact projection area A_(p) (nm²) are used tocalculate an indentation hardness from the value of P_(max)/A_(p). Thecontact projection area was a contact projection area, for which the tipcurvature of the indenter was corrected using fused quartz (5-0098,manufactured by BRUKER) as a standard sample in accordance with theOliver-Pharr method. The arithmetic mean of the measurements at 10different locations was determined as the indentation hardness (H_(IT)).In cases where the measurement values included a value deviating ±20% ormore from the arithmetic mean value, the deviating value was excluded,followed by remeasurement.

(Measurement Conditions)

-   -   loading speed: 20 μN/second;    -   retention time: 5 seconds;    -   unloading speed: 20 μN/second;    -   measurement temperature: 25° C.

<Check on Presence of Metallic Element and Metalloid Element, andMeasurement of Atomic Ratio of Total Amount of these Elements>

A check was made on whether at least one of a metallic element and ametalloid element was present in the hard coat layer of the optical filmaccording to each of Examples and Comparative Examples. Specifically, apiece having a size of 1 mm×6 mm was first cut out from the opticalfilm, and the piece was cut by approximately 200 nm in parallel with theplane using a microtome (product name “Ultramicrotome EM UC7”;manufactured by Leica Microsystems GmbH) to expose the hard coat layer.Then, an X-ray photoelectron spectroscope (ESCA, product name “KRATOSNova”; manufactured by Shimadzu Corporation) was used to carry outelemental analysis on the surface obtained by cutting asabove-described, whereby a check was made on whether the hard coat layercontained at least one of a metallic element and a metalloid element.When this was carried out, the atomic ratio (%) of the total amount ofthe metallic element and the metalloid element was also measured, usingan X-ray photoelectron spectroscope (ESCA, product name “KRATOS Nova”;manufactured by Shimadzu Corporation), on the surface obtained bycutting as above-described.

(Measurement Conditions)

-   -   measurement technique: Wide Narrow    -   X-ray source: monochrome AIKα    -   X-ray output: 150 W    -   emission current: 10 mA    -   accelerating voltage: 15 kV    -   charge-neutralization mechanism: ON    -   measurement region: 300×700 μm    -   Pass Energy (Survey): 160 eV    -   Pass Energy (Narrow): 40 eV

<Area Ratio of Silica Particles>

For the optical film according to each of Examples and ComparativeExamples, the area ratio of the inorganic particles was determined inthe interfacial region up to a depth of 500 nm into the hard coat layerfrom the interface between the hard coat layer and the inorganic layerin the cross-section of the hard coat layer in the film thicknessdirection. The area ratio of the inorganic particles in the interfacialregion was determined as below-mentioned. First of all, a piece of 1mm×10 mm cut out from the optical film was embedded in an embeddingresin to prepare a block, and 10 homogeneous sections having a thicknessof 70 nm or more and 100 nm or less and having no openings or the likewere cut out from the block according to a commonly used sectioningtechnique. For the preparation of sections, an “Ultramicrotome EM UC7”(Leica Microsystems GmbH) was used. Then, these 10 homogeneous sectionshaving no openings or the like were used as measurement samples. Then,the cross-sectional image of each measurement sample was acquired usinga scanning transmission electron microscope (STEM) (product name“S-4800”; manufactured by Hitachi High-Technologies Corporation). Here,the cross-section of one part per measurement sample was photographed.The cross-sectional images were acquired by setting the detector to“TE,” the accelerating voltage to “30 kV,” and the emission current to“10 μA” in the observation. The focus, contrast, and brightness wereappropriately adjusted at a magnification of 5000 to 200,000 times, sothat each layer could be identified by observation. Furthermore, thebeam monitor aperture, the objective lens aperture, and the WD wererespectively set to “3,” “3,” and “8 mm,” in acquirement ofcross-sectional images. Assuming that the area of the interfacial regionwas 100% in each of the obtained 10 cross-sectional images, the ratio(area ratio) of the area of the inorganic particles to the area of theinterfacial region was determined. The area ratio of the inorganicparticles to the interfacial region was the arithmetic mean value of thearea ratios of the organic particles determined from the 10cross-sectional images of the interfacial regions.

<Scratch Resistance>

The surface (surface of the inorganic layer) of the optical filmaccording to each of Examples and Comparative Examples was evaluated bycarrying out a steel wool test on the surface. Specifically, a piecehaving a size of 50 mm×100 mm was cut out from the optical film andfixed on a glass plate with Cello-Tape®, manufactured by Nichiban Co.,Ltd., so as to generate no fold or wrinkle and to have the inorganiclayer on the upper side. A steel wool test was carried out, in which thefixed piece was rubbed with steel wool with a grade of #0000 (productname “Bonstar”; manufactured by Nihon Steel Wool Co., Ltd.) byreciprocating the steel wool with a load of 1 kg/cm² for 10 times at aspeed of 50 mm/second, and the resulting surface of the optical film wasvisually checked for any scratch. The evaluation criteria were asbelow-mentioned.

∘: no scratch or chip was found, or a few scratches or chips were foundbut at a level which was not problematic for practical usage.

×: some clear scratches or chips were found.

<Measurement of Haze>

The haze value (total haze value) of the optical film according to eachof Examples and Comparative Examples was measured. The haze value wasmeasured using a haze meter (product name “HM-150”; manufactured byMurakami Color Research Laboratory Co., Ltd.) in accordance with JISK7136: 2000. The above-described haze value was defined as thearithmetic mean of three haze values, wherein the three haze values wereobtained by cutting a piece of 50 mm×100 mm from one optical film andplacing the piece of film without any curl or wrinkle and without anyfingerprint or dirt, into the haze meter in such a manner that theinorganic layer side faced opposite to the light source to measure thehaze value, and repeating the measurement three times.

<Total Light Transmittance>

The total light transmittance of the optical film according to each ofExamples and Comparative Examples was measured. The total lighttransmittance was measured using a haze meter (product name “HM-150”;manufactured by Murakami Color Research Laboratory Co., Ltd.) inaccordance with JIS K7361-1: 1997. The total light transmittance wasdefined as the arithmetic mean of three haze values, wherein the threehaze values were obtained by cutting a piece of 50 mm×100 mm from oneoptical film and placing the piece of film without any curl or wrinkleand without any fingerprint or dirt, into the haze meter in such amanner that the inorganic layer side faced opposite to the light sourceto measure the haze value, and repeating the measurement three times.

<Foldability>

The optical film according to each of Examples and Comparative Exampleswas evaluated for foldability by carrying out a folding test on theoptical film. Specifically, a piece having a size of 30 mm×100 mm wasfirst cut out from the optical film and mounted to an endurance testingmachine (product name “DLDMLH-FS”; manufactured by Yuasa System Co.,Ltd.) by fixing the short edges of the optical film piece to fixingmembers, as shown in FIG. 3(C), in such a manner that the minimumdistance between the two opposing edges was 6 mm, and the piece wastested by repeating the successive folding test (in which the piece wasfolded with the inorganic layer facing inward and with the polyimidebase material facing outward) one hundred thousand times, in each ofwhich the surface side of the optical film piece was folded inward at anangle of 180 degrees, to examine whether any crack or break was formedat the bent part. In the same manner, a new piece having a size of 30mm×100 mm was cut out from the optical film and mounted to an endurancetesting machine (product name “DLDMLH-FS”; manufactured by Yuasa SystemCo., Ltd.) by fixing the short edges of the optical film piece to fixingmembers, in such a manner that the minimum distance between the twoopposing edges was 2 mm, and the piece was tested by repeating thesuccessive folding test (in which the piece was folded with theinorganic layer facing inward and with the polyimide base materialfacing outward) one hundred thousand times, in each of which the surfaceside of the optical film piece was folded inward at an angle of 180degrees, to examine whether any crack or break was formed at the bentpart. The evaluation criteria were as below-mentioned.

(Foldability)

∘: no crack or break was formed at the bent part in the folding tests.

×: a crack(s) or a break(s) was/were formed at the bent part in thefolding tests.

<Interference Fringe Evaluation>

The optical film according to each of Examples and Comparative Exampleswas evaluated for interference fringe. Specifically, a piece having asize of 50 mm×100 mm was cut out from the optical film, and to the backsurface of the optical film piece, a black acrylic plate for preventingback surface reflection was attached via a transparent adhesive having athickness of 25 μm (product name “Optically Clear Adhesive 8146-1”;manufactured by 3M Company). The surface side of the optical film wasexposed to light and checked for any interference fringe by visualobservation. The light source used was a three-wavelength tubefluorescent lamp. The generation of interference fringe was rated on thebasis of the following criteria.

∘: no interference fringe was found.

Δ: slight interference fringe was found.

×: some interference fringe was clearly found.

TABLE 1 Metallic Element and Metalloid Area Element Ratio of HC FilmIndentation Atomic Silica Thickness Hardness present Ratio ParticleScratch (μm) (MPa) or not (%) (%) Resistance Example 1 4 587 yes 18.2 50○ Example 2 4 1010 yes 25.1 67 ○ Example 3 4 228 yes 3.2 6 ○ Example 4 4485 yes 16.4 51 ○ Example 5 1.2 574 yes 17.6 50 ○ Example 6 10 591 yes17.2 50 ○ Example 7 20 592 yes 17.3 51 ○ Example 8 4 588 yes 17 50 ○Example 9 4 589 yes 16.8 50 ○ Example 10 4 452 yes 6.8 — ○ ComparativeExample 1 4 320 no 0 0 x Comparative Example 2 4 125 yes 1 7 xComparative Example 3 0.8 572 yes 2.8 50 x

TABLE 2 Total Light Haze Value Transmittance Foldability (%) (%) 6 mm 2mm Interference Fringe Example 1 0.8 90.8 ∘ ∘ Δ Example 2 0.7 90.7 ∘ ∘ ΔExample 3 0.8 90.7 ∘ ∘ Δ Example 4 0.9 90.6 ∘ ∘ Δ Example 5 0.8 90.8 ∘ ∘Δ Example 6 0.8 90.8 ∘ ∘ Δ Example 7 0.8 90.8 ∘ x ∘ Example 8 0.7 90.8 ∘∘ ∘ Example 9 0.6 91.2 ∘ ∘ ∘ Example 10 0.4 91.1 ∘ ∘ ∘ ComparativeExample 1 0.7 91.1 ∘ ∘ Δ Comparative Example 2 0.6 91.0 ∘ ∘ ΔComparative Example 3 0.7 90.8 ∘ ∘ x

The results will be described below. As shown in Table 1, the hard coatlayer of the optical film according to Comparative Example 1 containedno inorganic particles, or did not contain at least one of a metallicelement and a metalloid element, and thus, the surface of the inorganiclayer was found to have low scratch resistance. The optical filmaccording to Comparative Example 2 had an indentation hardness of lessthan 200 MPa, and thus, the surface of the inorganic layer was found tohave low scratch resistance. The hard coat layer of the optical filmaccording to Comparative Example 3 had a small film thickness, and thus,the surface of the inorganic layer was found to have low scratchresistance. In contrast, the hard coat layer of the optical filmaccording to Examples 1 to 10 contained inorganic particles or at leastone of a metallic element and a metalloid element, the optical film hadan indentation hardness of 200 MPa or more, and the hard coat layer hada film thickness of 2 μm or more. Thus, the surface of the inorganiclayer was found to have excellent scratch resistance. In this regard, asteel wool test was carried out on the optical film according to each ofExamples 1 to 6 and 8 to 10 under the same conditions as above-describedafter the above-described folding test. Then, the surface of the opticalfilm was checked for any scratch and chip by visual observation, and theoptical films were found to have no scratch or chip, or have a fewscratches or chips but at a level which was not problematic forpractical usage.

The hard coat layer of the optical film according to each of Examples 1to 6 and 8 to 10 had a film thickness 10 μm or less, and thus, theoptical film had better foldability than the optical film according toExample 7 in which the hard coat layer had a film thickness of 20 μm.

The hard coat layer of the optical film according to Example 7 was quitethick, the optical film according to Example 8 had an optical adjustmentlayer formed therein, and the optical film according to Example 9 had apolyimide base material having low refractive index. Thus, none of theseoptical films were found to exhibit interference fringe.

The inorganic layer of the optical film according to each of Exampleswas checked for any silicon using an X-ray photoelectron spectroscope(product name “KRATOS Nova”; manufactured by Shimadzu Corporation), andall the optical films were found to have silicon present in theinorganic layer. To check whether the inorganic layer had siliconpresent therein, the surface of the inorganic layer of an optical filmcut to a size of 1 mm×6 mm was subjected to elemental analysis using anX-ray photoelectron spectroscope (ESCA, product name “KRATOS Nova”;manufactured by Shimadzu Corporation) under the same measurementconditions as a check was made on whether the hard coat layer had ametallic element and a metalloid element present therein.

LIST OF REFERENCE NUMERALS

-   -   10, 50: Optical film    -   11: Light-transmitting base material    -   12, 51: Hard coat layer    -   12A: Binder resin    -   12B: Inorganic particles    -   13: Inorganic layer    -   40, 60: Image display device    -   43: Display panel    -   51A: Silicone resin    -   51B: Inorganic particles

The invention claimed is:
 1. An optical film comprising alight-transmitting base material, a hard coat layer, and an inorganiclayer in this order, wherein the hard coat layer is in contact with theinorganic layer, the hard coat layer contains at least one of a metallicelement and a metalloid element, the hard coat layer has a filmthickness of 1 μm or more, the hard coat layer has an indentationhardness of 200 MPa or more, and the atomic ratio of the total of themetallic element and the metalloid element contained in the hard coatlayer is 1.5% or more and 30% or less as measured by X-ray photoelectronspectroscopy.
 2. The optical film according to claim 1, wherein the hardcoat layer contains a metalloid element, and the metalloid element issilicon.
 3. The optical film according to claim 1, wherein the inorganiclayer is an inorganic oxide layer.
 4. The optical film according toclaim 1, wherein the inorganic layer contains silicon.
 5. The opticalfilm according to claim 1, wherein the inorganic layer has a thicknessof 10 nm or more and 300 nm or less.
 6. The optical film according toclaim 1, wherein the hard coat layer contains a polymer of apolymerizable compound containing a silsesquioxane having apolymerizable functional group.
 7. The optical film according to claim1, wherein no crack or break is formed in the optical film after foldingthe optical film at an angle of 180 degrees in a manner that leaves agap of 6 mm between the opposite edges, unfolding the folded opticalfilm, and repeating the process one hundred thousand times.
 8. Theoptical film according to claim 1, wherein no crack or break is formedin the optical film after folding the optical film with the inorganiclayer facing inward at an angle of 180 degrees in a manner that leaves agap of 2 mm between the opposite edges, unfolding the folded opticalfilm, and repeating the process one hundred thousand times.
 9. Theoptical film according to claim 1, wherein the light-transmitting basematerial is composed of a polyimide resin, a polyamide resin, or acombination thereof.
 10. An image display device comprising a displaypanel and the optical film according to claim 1 placed on the observer'sside of the display panel, wherein the hard coat layer of the opticalfilm is placed on the observer's side of the light-transmitting basematerial.
 11. The image display device according to claim 10, whereinthe display panel is an organic light emitting diode panel.